The Webmaster's Lexicon: J

Java	A programming language designed for program execution on the client side, i.e. in a browser. Java is a simple, robust, object-oriented, platform-independent multi-threaded, dynamic general-purpose programming environment. It's best for creating applets and applications for the Internet, intranets and any other complex, distributed network.
JavaScript	A proprietary scripting language released by Netscape, JavaScript increases the aesthetics and friendliness of websites by adding author-specificed user events to static pages.
JPEG	Joint Photographic Experts Group, a popular cross-platform format for image files. The JPEG standard is an excellent standard for most realistic images (photos for example, but not line drawings or logos). It uses a powerful, though nominally "lossy," compression method (the resulting image may not be as rich as the original). JPEG is best suited for truecolor original images; avoid using it on images that have already been forced into a 256-color palette.