jQuery is an add-on library for JavaScript. Think of jQuery as JavaScript code that’s been written for you. In general, all you have to do is include a line or two of code in your page that calls the jQuery code. jQuery does the hard JavaScript coding work for you.
The jQuery framework itself has enjoyed a great deal of mainstream exposure. It has been used by Google, Dell, Digg, NBC, CBS, Netflix, The Mozilla Foundation, and the popular WordPress and Drupal PHP frameworks.
jQuery is fast — superfast — and it has a small footprint. It’s only 15 KB, using the compressed and gzipped version.
jQuery gives you the ability to provide complex, professional, visually driven user interfaces and effects with very few lines of code. What may have taken other developers days or even weeks to accomplish can be done with jQuery in just a few hours.