J

Java: An object-oriented programming language developed by Sun Microsystems. It's smaller and more versatile than C++, the popular programming language it's based on. It's useful for programming web applications, because it will run on any computer platform - Macintosh, UNIX, Windows, or DOS.

JavaScript: A scripting language developed by Netscape and Sun Microsystems that is loosely related to Java. JavaScript code can be included in a webpage along with HTML and is easier to write than Java. It is not a true programming language, though, and has limited functionality. In order for visitors to see the JavaScript on your site, they must have a browser that supports it, such as Netscape.
JK: Email and newsgroup abbreviation of "just kidding."

JPEG: Joint Photographic Experts Group (also JPG). A graphic file format, which stores images in a compressed form. They aren't as small or versatile as GIFs, but they offer better resolution, and are especially useful for photographs you want to display on the web or send via email.