jQuery is a fast, small, and feature-rich JavaScript library. It makes things like HTML document traversal and manipulation, event handling, animation, and Ajax much simpler with an easy-to-use API that works across a multitude of browsers.
Jquery is a JavaScript library. Okay, that might not make much sense. jquery also makes cross browser development easier. Though you haven’t seen much of it so far, support for JavaScript differs widely from browser to browser and from version to version.