The alt attribute is used to define an "alternate text" for an image. The value of the alt attribute is an author-defined text.
A small Java program that can be embedded in an HTML page. Applets differ from full-fledged Java applications in that they are not allowed to access certain resources on the local computer, such as files and serial devices (modems, printers, etc.), and are prohibited from communicating with most other computers across a network. The common rule is that an applet can only make an Internet connection to the computer from which the applet was sent.
Server software that manages one or more other pieces of software in a way that makes the managed software available over a network, usually to a Web server. By having a piece of software manage other software packages it is possible to use resources like memory and database access more efficiently than if each of the managed packages responded directly to requests.
How much stuff you can send through a connection. Usually measured in bits-per-second (bps.) A full page of English text is about 16,000 bits. A fast modem can move about 57,000 bits in one second. Full-motion full-screen video would require roughly 10,000,000 bits-per-second, depending on compression.
Blog -- (weB LOG)
A blog is basically a journal that is available on the web. The activity of updating a blog is "blogging" and someone who keeps a blog is a "blogger." Blogs are typically updated daily using software that allows people with little or no technical background to update and maintain the blog.
Postings on a blog are almost always arranged in chronological order with the most recent additions featured most prominently.
It is common for blogs to be available as RSS feeds.
Blogosphere or Blogsphere
The current state of all information available on blogs and/or the sub-culture of those who create and use blogs.
bps -- (Bits-Per-Second)
A measurement of how fast data is moved from one place to another. A 56K modem can move about 57,000 bits per second.
A Client program (software) that is used to look at various kinds of Internet resources.
A set of Bits that represent a single character. Usually there are 8 Bits in a Byte, sometimes more, depending on how the measurement is being made.
An issuer of Security Certificates used in SSL connections.
A software program that is used to contact and obtain data from a Server software program on another computer, often across a great distance. EachClient program is designed to work with one or more specific kinds of Server programs, and each Server requires a specific kind of Client. A Web Browser is a specific kind of Client.
The most common meaning of "Cookie" on the Internet refers to a piece of information sent by a Web Server to a Web Browser that the Browser software is expected to save and to send back to the Server whenever the browser makes additional requests from the Server.
Depending on the type of Cookie used, and the Browsers' settings, the Browser may accept or not accept the Cookie, and may save the Cookie for either a short time or a long time.
Cookies might contain information such as login or registration information, online "shopping cart" information, user preferences, etc.
When a Server receives a request from a Browser that includes a Cookie, the Server is able to use the information stored in the Cookie. For example, the Server might customize what is sent back to the user, or keep a log of particular users' requests.
Cookies are usually set to expire after a predetermined amount of time and are usually saved in memory until the Browser software is closed down, at which time they may be saved to disk if their "expire time" has not been reached.
Cookies do not read your hard drive and send your life story to the CIA, but they can be used to gather more information about a user than would be possible without them.
CSS -- (Cascading Style Sheet)
A standard for specifying the appearance of text and other elements. CSS was developed for use with HTML in Web pages but is also used in other situations, notably in applications built using XPFE. CSS is typically used to provide a single "library" of styles that are used over and over throughout a large number of related documents, as in a web site. A CSS file might specify that all numbered lists are to appear in italics. By changing that single specification the look of a large number of documents can be easily changed.
DNS -- (Domain Name System)
The Domain Name System is the system that translates Internet domain names into IP numbers. A "DNS Server" is a server that performs this kind of translation.
The unique name that identifies an Internet site. Domain Names always have 2 or more parts, separated by dots. The part on the left is the most specific, and the part on the right is the most general. A given machine may have more than one Domain Name but a given Domain Name points to only one machine. For example, the domain names:
can all refer to the same machine, but each domain name can refer to no more than one machine.
Usually, all of the machines on a given Network will have the same thing as the right-hand portion of their Domain Names (matisse.net in the examples above). It is also possible for a Domain Name to exist but not be connected to an actual machine. This is often done so that a group or business can have an Internet e-mail address without having to establish a real Internet site. In these cases, some real Internet machine must handle the mail on behalf of the listed Domain Name.
Transferring data (usually a file) from a another computer to the computer you are are using. The opposite of upload.
Email -- (Electronic Mail)
Messages, usually text, sent from one person to another via computer. E-mail can also be sent automatically to a large number of addresses.
A very common method of networking computers in a LAN. There is more than one type of Ethernet. By 2001 the standard type was "100-BaseT" which can handle up to about 100,000,000 bits-per-second and can be used with almost any kind of computer.
An intranet that is accesible to computers that are not physically part of a companys' own private network, but that is not accessible to the general public, for example to allow vendors and business partners to access a company web site.
Often an intranet will make use of a Virtual Private Network. (VPN.)
A combination of hardware and software that separates a Network into two or more parts for security purposes.
FTP -- (File Transfer Protocol)
A very common method of moving files between two Internet sites.
FTP is a way to login to another Internet site for the purposes of retrieving and/or sending files. There are many Internet sites that have established publicly accessible repositories of material that can be obtained using FTP, by logging in using the account name "anonymous", thus these sites are called "anonymous ftp servers".
FTP was invented and in wide use long before the advent of the World Wide Web and originally was always used from a text-only interface.
1000 or 1024 Megabytes, depending on who is measuring.
The <h1> to <h6> tags are used to define HTML headings.
<h1> defines the largest heading and <h6> defines the smallest heading.
As used in reference to the World Wide Web, ?hit? means a single request from a web browser for a single item from a web server; thus in order for a web browser to display a page that contains 3 graphics, 4 ?hits? would occur at the server: 1 for the HTML page, and one for each of the 3 graphics.
Home Page (or Homepage)
Several meanings. Originally, the web page that your browser is set to use when it starts up. The more common meaning refers to the main web page for a business, organization, person or simply the main page out of a collection of web pages, e.g. "Check out so-and-so's new Home Page."
Any computer on a network that is a repository for services available to other computers on the network. It is quite common to have one host machine provide several services, such as SMTP (email) and HTTP (web).
HTML -- (HyperText Markup Language)
The coding language used to create Hypertext documents for use on the World Wide Web. HTML looks a lot like old-fashioned typesetting code, where you surround a block of text with codes that indicate how it should appear.
The "hyper" in Hypertext comes from the fact that in HTML you can specify that a block of text, or an image, is linked to another file on the Internet. HTML files are meant to be viewed using a "Web Browser".
HTML is loosely based on a more comprehensive system for markup called SGML, and is expected to eventually be replaced by XML-based XHTML standards.
HTTP -- (HyperText Transfer Protocol)
The protocol for moving hypertextfiles across the Internet. Requires a HTTP client program on one end, and an HTTP server program (such as Apache) on the other end. HTTP is the most important protocol used in the World Wide Web (WWW).
internet (Lower case i)
Any time you connect 2 or more networks together, you have an internet - as in inter-national or inter-state.
Internet (Upper case I)
The vast collection of inter-connected networks that are connected using the TCP/IP protocols and that evolved from the ARPANET of the late 60's and early 70's.
The Internet connects tens of thousands of independent networks into a vast global internet and is probably the largest Wide Area Network in the world.
A private network inside a company or organization that uses the same kinds of software that you would find on the public Internet, but that is only for internal use. Compare with extranet.
IP Number -- (Internet Protocol Number)
Sometimes called a dotted quad. A unique number consisting of 4 parts separated by dots, e.g.188.8.131.52
Every machine that is on the Internet has a unique IP number - if a machine does not have an IP number, it is not really on the Internet. Many machines (especially servers) also have one or more Domain Names that are easier for people to remember.
ISP -- (Internet Service Provider)
An institution that provides access to the Internet in some form, usually for money.
Java is a network-friendly programming language invented by Sun Microsystems.
Java is often used to build large, complex systems that involve several different computers interacting across networks, for example transaction processing systems.
Java is also used to create software with graphical user interfaces such as editors, audio players, web browsers, etc.
Java is also popular for creating programs that run in small electronic devicws, such as mobile telephones.
Using small Java programs (called "Applets"), Web pages can include functions such as animations, calculators, and other fancy tricks.
JPEG -- (Joint Photographic Experts Group)
JPEG is most commonly mentioned as a format for image files. JPEG format is preferred to the GIF format for photographic images as opposed to line art or simple logo art.
JDK -- (Java Development Kit)
A software development package from Sun Microsystems that implements the basic set of tools needed to write, test and debugJava applications and applets
JPEG -- (Joint Photographic Experts Group)
JPEG is most commonly mentioned as a format for image files. JPEG format is preferred to the GIF format for photographic images as opposed to line art or simple logo art.
A thousand bytes. Actually, usually 1024 (210) bytes.
LAN -- (Local Area Network)
A computer network limited to the immediate area, usually the same building or floor of a building.
Refers to line such as a telephone line or fiber-optic cable that is rented for exclusive 24-hour, 7-days-a-week use from your location to another location. The highest speed data connections require a leased line.
A widely used Open Source Unix-like operating system. Linux was first released by its inventor Linus Torvalds in 1991. There are versions of Linux for almost every available type of computer hardware from desktop machines to IBM mainframes. The inner workings of Linux are open and available for anyone to examine and change as long as they make their changes available to the public. This has resulted in thousands of people working on various aspects of Linux and adaptation of Linux for a huge variety of purposes, from servers to TV-recording boxes.
Noun: The account name used to gain access to a computer system. Not a secret (contrast with Password).
Verb: the act of connecting to a computer system by giving your credentials (usually your "username" and "password")
(or Mailing List) A (usually automated) system that allows people to send e-mail to one address, whereupon their message is copied and sent to all of the other subscribers to the maillist. In this way, people who have many different kinds of e-mail access can participate in discussions together.
A web page or site made by automatically combining content from other sources, usually by using material available via RSS feeds and/or REST interfaces.
Technically speaking, a million bytes. In many cases the term means 1024 kilobytes, which is a more than an even million.
A specific kind of HTML tag that contains information not normally displayed to the user. Meta tags contan information about the page itself, hence the name ("meta" means "about this subject")
Typical uses of Meta tags are to include information for search engines to help them better categorize a page. You can see the Meta tags in a page if you view the pages' source code.
Generally speaking, "to mirror" is to maintain an exact copy of something. Probably the most common use of the term on the Internet refers to "mirror sites" which are web sites, or FTP sites that maintain copies of material originated at another location, usually in order to provide more widespread access to the resource. For example, one site might create a library of software, and 5 other sites might maintain mirrors of that library.
A WWW Browser and the name of a company. The Netscape (tm) browser was originally based on the Mosaic program developed at the National Center for Supercomputing Applications (NCSA).
Any time you connect 2 or more computers together so that they can share resources, you have a computer network. Connect 2 or more networks together and you have an internet.
The name for discussion groups on USENET.
NIC -- (Network Information Center)
Generally, any office that handles information for a network. The most famous of these on the Internet was the InterNIC, which was where most new domain names were registered until that process was decentralized to a number of private companies. Also means "Network Interface card", which is the card in a computer that you plug a network cable into.
Any single computer connected to a network.
Copyrighted information (such as this Glossary) that is made available by the copyright owner to the general public under license terms that allow reuse of the material, often with the requirement (as with this Glossary) that the re-user grant the public the same rights to the modified version that the re-user received from the copyright owner.
Information that is in the Public Domain might also be considered a form of Open Content.
Open Source Software
Open Source Software is software for which the underlying programming code is available to the users so that they may read it, make changes to it, and build new versions of the software incorporating their changes. There are many types of Open Source Software, mainly differing in the licensing term under which (altered) copies of the source code may (or must be) redistributed.
A code used to gain access (login) to a locked system. Good passwords contain letters and non-letters and are not simple combinations such as virtue7. A good password might be: 5%df(29) But don't use that one!
PDF -- (Portable Document Format)
A file format designed to enable printing and viewing of documents with all their formatting (typefaces, images, layout, etc.) appearing the same regardless of what operating system is used, so a PDF document should look the same on Windows, Macintosh, linux, OS/2, etc. The PDF format is based on the widely used Postcript document-description language. Both PDF and Postscript were developed by the Adobe Corporation.
A "permanent link" to a particular posting in a blog. A permalink is a URI that points to a specific blog posting, rather than to the page in which the posting original occured (which may no longer contain the posting.)
PHP -- (PHP: Hypertext Preprocessor)
PHP is a programming language used almost exclusively for creating software that is part of a web site. The PHP language is designed to be intermingled with the HTML that is used to create web pages. Unlike HTML, the PHP code is read and processed by the web server software (HTML is read and processed by the web browser software.)
A (usually small) piece of software that adds features to a larger piece of software. Common examples are plug-ins for the Netscape browser and web server. Adobe Photoshop also uses plug-ins.
PNG -- (Portable Network Graphics)
PNG is a graphics format specifically designed for use on the World Wide Web. PNG enable compression of images without any loss of quality, including high-resolution images. Another important feature of PNG is that anyone may create software that works with PNG images without paying any fees - the PNG standard is free of any licensing costs.
Podcasting or Pod-casting
A form of audio broadcasting using the Internet, podcasting takes its name from a combination of "iPod" and broadcasting. iPod is the immensely popular digital audio player made by Apple computer, but podcasting does not actually require the use of an iPod.
Podcasting involves making one or more audio files available as "enclosures" in an RSS feed. A pod-caster creates a list of music, and/or other sound files (such as recorded poetry, or "talk radio" material) and makes that list available in the RSS 2.0 format. The list can then be obtained by other people using various podcast "retriever" software which read the feed and makes the audio files available to digital audio devices (including, but not limited to iPods) where users may then listen to them at their convenience.
POP -- (Point of Presence, also Post Office Protocol)
Two commonly used meanings: Point of Presence and Post Office Protocol.
A Point of Presence usually means a city or location where a network can be connected to, often with dial up phone lines. So if an Internet company says they will soon have a POP in Belgrade, it means that they will soon have a local phone number in Belgrade and/or a place where leased lines can connect to their network.
A second meaning, Post Office Protocol refers to a way that e-mail client software such as Eudora gets mail from a mail server. When you obtain an account from an Internet Service Provider (ISP) you almost always get a POP account with it, and it is this POP account that you tell your e-mail software to use to get your mail. Another protocol called IMAP is replacing POP for email.
3 meanings. First and most generally, a place where information goes into or out of a computer, or both. E.g. the serial port on a personal computer is where a modem would be connected.
On the Internet port often refers to a number that is part of a URL, appearing after a colon (:) right after the domain name. Every service on an Internet server listens on a particular port number on that server. Most services have standard port numbers, e.g. Web servers normally listen on port 80. Services can also listen on non-standard ports, in which case the port number must be specified in a URL when accessing the server, so you might see a URL of the form:
This shows a gopher server running on a non-standard port (the standard gopher port is 70). Finally, port also refers to translating a piece of software to bring it from one type of computer system to another, e.g. to translate a Windows program so that is will run on a Macintosh.
Usually used as a marketing term to described a Web site that is or is intended to be the first place people see when using the Web. Typically a "Portal site" has a catalog of web sites, a search engine, or both. A Portal site may also offer email and other service to entice people to use that site as their main "point of entry" (hence "portal") to the Web.
A single message entered into a network communications system.
On the Internet "protocol" usually refers to a set of rules that define an exact format for communication between systems. For example the HTTP protocol defines the format for communication between web browsers and web servers, the IMAP protocol defines the format for communication between IMAP email servers and clients, and the SSL protocol defines a format for encrypted communications over the Internet.
A Proxy Server sits in between a Client and the "real" Server that a Client is trying to use. Client's are sometimes configured to use a Proxy Server, usually an HTTP server. The clients makes all of it's requests from the Proxy Server, which then makes requests from the "real" server and passes the result back to the Client. Sometimes the Proxy server will store the results and give a stored result instead of making a new one (to reduce use of a Network). Proxy servers are commonly established on Local Area Networks proposal is reviewed by the Internet Engineering Task Force (http://www.ietf.org/), a consensus-building body that facilitates discussion, and eventually a new standard is established, but the reference number/name for the standard retains the acronym RFC, e.g. the official standard for e-mail message formats is RFC 822.
A special-purpose computer (or software package) that handles the connection between 2 or more Packet-Switched networks. Routers spend all their time looking at the source and destination addresses of the packets passing through them and deciding which route to send them on.
A (usually web-based) system for searching the information available on the Web. Some search engines work by automatically searching the contents of other systems and creating a database of the results. Other search engines contains only material manually approved for inclusion in a database, and some combine the two approaches.
A chunk of information (often stored as a text file) that is used by the SSL protocol to establish a secure connection.
SEO -- (Search Engine Optimization)
The practice of designing web pages so that they rank as high as possible in search results from search engines.
There is "good" SEO and "bad" SEO. Good SEO involves making the web page clearly describe its subject, making sure it contains truly useful information, including accurate information in Meta tags, and arranging for other web sites to make links to the page. Bad SEO involves attempting to deceive people into believing the page is more relevant than it truly is by doing things like adding inaccurate Meta tags to the page.
A computer, or a software package, that provides a specific kind of service to client software running on other computers. The term can refer to a particular piece of software, such as a WWW server, or to the machine on which the software is running, e.g. "Our mail server is down today, that's why e-mail isn't getting out."
A single server machine can (and often does) have several different server software packages running on it, thus providing many different servers to clients on the network.
Sometimes server software is designed so that additional capabilities can be added to the main program by adding small programs known as servlets.
A small computer program designed to be add capabilities to a larger piece of server software.Common examples are "Java servlets", which are small programs written in the Java language and which are added to a web server. Typically a web server that uses Java servlets will have many of them, each one designed to handle a very specific situation, for example one servlet will handle adding items to a "shopping cart", while a different servlet will handle deleting items from the "shopping cart."
SMTP -- (Simple Mail Transfer Protocol)
The main protocol used to send electronic mail from server to server on the Internet. SMTP is defined in RFC 821 and modified by many later RFC's.
Spam (or Spamming)
An inappropriate attempt to use a mailing list, or USENET or other networked communications facility as if it was a broadcast medium (which it is not) by sending the same message to a large number of people who didn?t ask for it. The term probably comes from a famous Monty Python skit which featured the word spam repeated over and over. The term may also have come from someone's low opinion of the food product with the same name, which is generally perceived as a generic content-free waste of resources. (Spam is a registered trademark of Hormel Corporation, for its processed meat product.)
A somewhat vague term generally referring to software that is secretly installed on a users computer and that monitors use of the computer in some way without the users' knowledge or consent.
Most spyware tries to get the user to view advertising and/or particular web pages. Some spyware also sends information about the user to another machine over the Internet.
Spyware is usually installed without a users' knowledge as part of the installation of other software, especially software such as music sharing software obtained via download.
SQL -- (Structured Query Language)
A specialized language for sending queries to databases. Most industrial-strength and many smaller database applications can be addressed using SQL. Each specific application will have its own slightly different version of SQL implementing features unique to that application, but all SQL-capable databases support a common subset of SQL.
A example of an SQL statement is:
SELECT name,email FROM people_table WHERE contry='uk'
SSL -- (Secure Socket Layer)
A protocol designed by Netscape Communications to enable encrypted, authenticated communications across the Internet.
A leased-line connection capable of carrying data at 1,544,000 bits-per-second. At maximum theoretical capacity, a T-1 line could move a megabyte in less than 10 seconds. That is still not fast enough for full-screen, full-motion video, for which you need at least 10,000,000 bits-per-second. T-1 lines are commonly used to connect large LANs to theInternet.
A leased-line connection capable of carrying data at 44,736,000 bits-per-second. This is more than enough to do full-screen, full-motionvideo.
The term "tag" can be used as a noun or verb. As a noun, a tag is a basic element of the languages used to create web pages (HTML) and similar languages such as XML. Another, more recent meaning of tag is related to reader-crearted tags where blogs and other content (such as photos, music, etc.) may be "tagged" which means to assign a keyword, such as "politics" or "gardening", this enables searches for "all the blog postings in the past week that are tagged 'prenatal care'"
A device that allows you to send commands to a computer somewhere else. At a minimum, this usually means a keyboard and a display screen and some simple circuitry. Usually you will use terminal software in a personal computer - the software pretends to be (emulates) a physical terminal and allows you to type commands to a computer somewhere else.
A special purpose computer that has places to plug in many modemson one side, and a connection to a LAN or host machine onthe other side. Thus the terminal server does the work of answering the calls and passes the connections on to the appropriate node. Most terminal servers can provide PPP or SLIP services if connected to the Internet.
TLD -- (Top Level Domain)
The last (right-hand) part of a complete Domain Name. For example in the domain name www.matisse.net ".net" is the Top Level Domain. There are a large number of TLD's, for example .biz, .com, .edu, .gov, .info, .int, .mil, .net, .org, and a collection of two-letter TLD's corresponding to the standard two-letter country codes, for example, .us, .ca, .jp, etc.
A computer program is either hidden inside another program or that masquerades as something it is not in order to trick potential users into running it. For example a program that appears to be a game or image file but in reality performs some other function. The term "Trojan Horse" comes from a possibly mythical ruse of war used by the Greeks sometime between 1500 and 1200 B.C.
A Trojan Horse computer program may spread itself by sending copies of itself from the host computer to other computers, but unlike a virus it will (usually) not infect other programs.
A computer operating system (the basic software running on a computer, underneath things like word processors and spreadsheets). Unix is designed to be used by many people at the same time (it is multi-user) and has TCP/IP built-in. It is the most common operating system for servers on the Internet. Apple computers' Macintosh operating system, as of version 10 ("Mac OS X"), is based on Unix.
Transferring data (usually a file) from a the computer you are using to another computer. The opposite of download.
URI -- (Uniform Resource Identifier)
An address for s resource available on the Internet. The first part of a URI is called the "scheme". the most well known scheme is http, but there are many others. Each URI scheme has its own format for how a URI should appear.
Here are examples of URIs using the http, telnet, and news schemes:
URL -- (Uniform Resource Locator)
The term URL is basically synonymous with URI. URI has replaced URL in technical specifications.
A chunk of computer programming code that makes copies of itself without any concious human intervention. Some viruses do more than simply replicate themselves, they might display messages, install other software or files, delete software of files, etc.
A virus requires the presence of some other program to replicate itself. Typically viruses spread by attaching themselves to programs and in some cases files, for example the file formats for Microsoft word processor and spreadsheet programs allow the inclusion of programs called "macros" which can in some cases be a breeding ground for viruses.
VOIP -- (Voice Over IP)
A specification and various technologies used to allow making telephone calls over IP networks, especially the Internet.
Just as modems allow computers to connect to the Internet over regular telephone lines, VOIP technology allows humans to talk over Internet connections.
Costs for VOIP calls can be a lot lower than for traditional telephone calls. Because the IP networks are packet-switched this allows for vastly different ways of handling connections and more efficient use of network resources.
VPN -- (Virtual Private Network)
Usually refers to a network in which some of the parts are connected using the public Internet, but the data sent across the Internet is encrypted, so the entire network is "virtually" private.
WAN -- (Wide Area Network)
Any internet or network that covers an area larger than a single building or campus.
Short for "World Wide Web."
A document designed for viewing in a web browser. Typically written in HTML. A web site is made of one or more web pages.
The entire collection of web pages and other information (such as images, sound, and video files, etc.) that are made available through what appears to users as a single web server. Typically all the of pages in a web site share the same basic URL, for example the following URLs are all for pages within the same web site:
The term has a somewhat informal nature since a large organization might have separate "web sites" for each division, but someone might talk informally about the organizations' "web site" when speaking of all of them.
Wi-Fi -- (Wireless Fidelity)
A popular term for a form of wireless data communication, basically Wi-Fi is "Wireless Ethernet".
A wiki is a web site for which the content can be easily edited and altered from the web browser in which you are viewing it. Typically there is an "edit" button on each page and the wiki is configured to allow either anyone or only people with passwords to edit each page. The word "wiki" comes from a Hawaiian word meaning "quick."
A worm is a virus that does not infect other programs. It makes copies of itself, and infects additional computers (typically by making use of network connections) but does not attach itself to additional programs; however a worm might alter, install, or destroy files and programs.
WWW -- (World Wide Web)
World Wide Web (or simply Web for short) is a term frequently used (incorrectly) when referring to "The Internet", WWW has two major meanings:
First, loosely used: the whole constellation of resources that can be accessed using Gopher, FTP, HTTP,telnet, USENET, WAIS and some other tools.
Second, the universe of hypertext servers (HTTP servers), more commonly called "web servers", which are the servers that serve web pages to web browsers.
XHTML -- (eXtensible HyperText Markup Language)
Basically HTML expressed as valid XML. XHTML is intended to be used in the same places you would use HTML (creating web pages) but is much more strictly defined, which makes it a lot easier to create sofware that can read it, edit it, check it for errors, etc.
XHTML is expected to eventually replace HTML.
XML -- (eXtensible Markup Language)
A widely used system for defining data formats. XML provides a very rich system to define complex documents and data structures such as invoices, molecular data, news feeds, glossaries, inventory descriptions, real estate properties, etc.
As long as a programmer has the XML definition for a collection of data (often called a "schema") then they can create a program to reliably process any data formatted according to those rules.
XML is a subset of the older SGML specification - the definition of XML is SGML minus a couple of dozen items.
using the XUL language.