HTML - Hyper Text Markup Language
Web pages are written in hypertext, this is not because the text moves quickly, but rather because it can interact (a little) with the reader. A book (or a Word document) will always stay the same each time you read it, but hypertext is meant to be easily changed and manipulated so that it could ultimately be Dynamic.
DHTML or dHTML - Dynamic HTML
DOM - Document Object Model
CSS - Cascading Style Sheets
Style sheets are directives for browsers to display Web pages exactly how the designer would like to display them. They allow for very specific control over the look and feel of a Web page.
XML - eXtensible Markup Language
This is a markup language that allows developers to develop their own markup language. For more information, I would read my article XML Explained.
URL - Uniform Resource Locator (some say Universal Resource Locator)
This is the Web page address. The Internet works very much like the post office in that it needs an address to send information to and from. The URL is the address that the Web uses.
HTTP - Hyper Text Transfer Protocol (some say Hyper Text Transport Protocol)
Basically, when you see this in a URL, all it means is Web Page. However, it is officially the method that the "post office" uses to send your Web page from it's home to your Web browser. It is the way the "hypertext" (Web page information) is transferred to your computer.
FTP - File Transfer Protocol
When you see this in a URL it usually means that instead of a Web server machine on the other end, you are connecting to a file server machine. For our purposes, the difference between ftp:// and http:// is that FTP usually means that something will be saved to your hard drive.