All definitions below are quoted from Wikipedia.

Address Bar - An URL bar, or location bar/address bar, is a widget in a web browser which indicates the URL of the webpage currently viewed. A new page can be viewed by typing its URL to the URL bar.

Extension - A filename extension is an extra set of (usually) alphanumeric characters that is appended to the end of a filename to allow computer users (as well as various pieces of software on the computer system) to quickly determine the type of data stored in the file. It is one of several popular methods for distinguishing between file formats.

File Transfer Protocol - FTP or file transfer protocol is a protocol used for exchanging files over the Internet. FTP works in the same way as HTTP for transferring Web pages from a server to a user's browser, and SMTP for transferring electronic mail across the Internet in that FTP uses the Internet's TCP/IP protocols to enable data transfer. FTP is most commonly used to download a file from a server using the Internet or to upload a file to a server (e.g., uploading a Web page file to a server).

File type (format) - A file format is a particular way to encode information for storage in a computer file.

GIF - GIF (Graphics Interchange Format) is a bitmap image format for pictures that use 256 (or fewer) distinct colors (though there is a workaround for this limitation) and animations that use 256 (or fewer) distinct colors per frame. GIFs are compressed files, and are employed specifically to reduce the amount of time it takes to transfer images over a network connection. The format was introduced by CompuServe in 1987 and has since come into widespread usage on the World Wide Web.

Graphical User Interface - GUI - A graphical user interface (or GUI, sometimes pronounced "gooey") is a method of interacting with a computer through a metaphor of direct manipulation of graphical images and widgets in addition to text.

HTML Tags - In computing, an HTML element indicates structure in an HTML document. More specifically, it is an SGML element that meets the requirements of one or more of the HTML Document Type Definitions (DTDs). HTML elements generally consist of three parts: a start tag marking the beginning of an element, some amount of content, and an end tag. Elements may represent headings, paragraphs, hypertext links, lists, embedded media, and a variety of other structures.

HyperText Markup Language - In computing, HyperText Markup Language (HTML) is a markup language designed for the creation of web pages and other information viewable in a browser. HTML is used to structure information -- denoting certain text as headings, paragraphs, lists and so on -- and can be used to define the semantics of a document.

Installer - An installation program or installer is a computer program that installs files, such as applications, drivers, or other software, onto a computer. Some installers are specifically made to install the files they contain; other installers are general-purpose and work by reading the contents of the software package to be installed.

JPEG (compression) - In computing, JPEG (pronounced jay-peg) is a commonly used standard method of lossy compression for photographic images. The file format which employs this compression is commonly also called JPEG; the most common file extensions for this format are .jpeg, .jfif, .jpg, .JPG, or .JPE although .jpg is the most common on all platforms.

Kilobyte - A kilobyte (derived from the SI prefix kilo-) is a unit of information or computer storage equal to either 1024 or 1000 bytes. It is commonly abbreviated KB, kB, Kbyte, kbyte, or very informally, K or k.

Megabyte - A megabyte is a unit of information or computer storage equal to approximately one million bytes. Megabyte is commonly abbreviated as MB (not to be confused with Mb, which is used for megabits), and sometimes as meg.

Mirror (computing) - A mirror in computing is a direct copy of a data set. On the Internet, a mirror site is an exact copy of another Internet site (often a web site). Mirror sites are most commonly used to provide multiple sources of the same information, and are of particular value as a way of providing reliable access to large downloads.

Open Source software - "Open source software refers to computer software and the availability of its source code as open source under an open source license to study, change, and improve its design.

Path - A path is the general form of a file or directory name, giving a file's name and its unique location in a file system. Paths point to their location using a string of characters signifying directories, separated by a delimiting character, most commonly the slash "/" or backslash character "\", though some operating systems may use a different delimiter.

Plain Text - In computing, plain text is textual material, usually in a disk file, that is (largely) unformatted. Thus, "I'm keeping that letter in plain text form until someone insists on getting it in the Foo format".

Relative Path - A relative path is a path relative to the current working directory, so the full absolute path may not need to be given.

Text Editor - A text editor is a piece of computer software for editing plain text. It is distinguished from a word processor in that it does not manage document formatting or other features commonly used in desktop publishing.

URL - A Uniform Resource Locator, URL (properly pronounced as a spelled-out initialism, not syllabized as 'earl'), or Web address, is a standardized address name layout for resources (such as documents or images) on the Internet (or elsewhere).

Web Browser - A web browser is a software application that enables a user to display and interact with HTML documents hosted by web servers or held in a file system. Popular browsers available for personal computers include Microsoft Internet Explorer, Mozilla Firefox, Opera, Netscape, Safari and Konqueror. A browser is the most commonly used kind of user agent. The largest networked collection of linked documents is known as the World Wide Web.

Web Server - A computer that is responsible for accepting HTTP requests from clients, which are known as web browsers, and serving them web pages, which are usually HTML documents.

WYSIWYG - WYSIWYG (pronounced "wizzy-wig" or "wuzzy-wig") is an acronym for What You See Is What You Get, and is used in computing to describe a system in which content during editing appears very similar to the final product. It is commonly used for word processors, but has other applications, such as Web (HTML) authoring.