JS stands for JavaScript. It's mainly used on web sites to bring functionality to HTML. When they're used together, JS and HTML can be extremely useful.
If you need more information, I would suggest reading the JavaScript Tutorial on howtocreate, it's good reading.
Javascript and Java are unrelated. The only thing that they have in common is the name. (Javascript was once known as LiveScript, but Netscape changed the name when it became clearthat Java was going to become a major trend.)
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