A loosely typed, object-oriented language formerly and officialy known as ECMAScript. JavaScript is often found embedded in webpages to enhance functionality. The majority of web browsers support JavaScript, including Internet Explorer, Mozilla, Konqueror, Links and Opera to name a few.
Note that JavaScript is not Java, although the two may communicate with eath other via a protocol known as LiveConnect.
External links
ECMAScript Language Specification
Free JavaScript tutorials, reference, code, and help
W3Schools.com JavaScript Tutorials
Tips & Tricks - "... studying and defeating browser incompatibilities. ..."