Javascript is a client-side scripting language for web pages. Read this The only thing common between javascript and java is the name
Java is more a single-paradigm(maybe not technically but effectively) language(object-oriented) where Javascript is more of a multiple-paradigm language. Javascript may actually be a nicer language(if you ignore all the core Java libraries and the fact that it compiles to an intermediate code). Javascript has aspects of the object oriented paradigm, the imperative paradigm and also the functional paradigm. Javascript is based on the same language standard as Adobe's Actionscript, which also seems like a really cool language. I'm just starting to get into it but I think I'm going to like it.
oh, sorry, but too many strange question of this kind today... What is the PHP? What is the Javascript? Why people don't ask what is the HTML or CSS? How old are you? You should invest your time and money and buy a book for web beginners. Sorry for OT. Answer to your question: http://en.wikipedia.org/wiki/JavaScript
Here's a little more advanced explanation of Javascript. http://video.google.com/videoplay?d...javascript+language&ei=xLlqSOmQD6j0qgOam82OBA
Learn to use google, stop asking really basic questions. Use wikipedia as well. "What is wikipedia ?" - sigh