jQuery
jQuery is a lightweight JavaScript library that emphasizes interaction between JavaScript and HTML. It was released in January 2006 at BarCamp NYC by John Resig.

jQuery is free, open source software Dual-licensed under the MIT License and the GNU General Public License.

Microsoft and Nokia have announced plans to bundle jQuery on their platforms, Microsoft adopting it initially within Visual Studio for use within Microsoft's ASP.NET AJAX framework and ASP.NET MVC Framework whilst Nokia will integrate it into their Web Run-Time platform.

jQuery Features
jQuery contains the following features:

1. DOM element selections using the cross-browser open source selector engine Sizzle, a spin-off out of the jQuery project
2. DOM traversal and modification (including support for CSS 1-3 and basic XPath)
3. Events
4. CSS manipulation
5. Effects and animations
6. Ajax
7. Extensibility
8. Utilities - such as browser version and the each function.

jQuery usually exists as a single JavaScript file, containing all the common DOM, Event, Effects, and Ajax functions. It can be included within a web page using the following mark-up:
<script type= "application/javascript" src="jQuery.js"></script>

jQuery can also be accessed, loaded, and run just as JavaScript has always been
<script type="text/javascript" src="jQuery.js"></script>

jQuery can also be loaded using the Google AJAX Libraries API with the following mark-up
<script type="application/javascript" src="http://www.google.com/jsapi">
</script>
<script>
google.load("jquery", "1.3.2");
</script>