What is jQuery?
jQuery is a fast and concise JavaScript Library created by John Resig in 2006 with a nice motto: Write less, do more. jQuery simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is a JavaScript toolkit designed to simplify various tasks by writing less code. Here is the list of important core features supported by jQuery:
 DOM manipulation: The jQuery made it easy to select DOM elements, negotiate them and modifying their content by using cross-browser open source selector engine called Sizzle.
 Event handling: The jQuery offers an elegant way to capture a wide variety of events, such as a user clicking on a link, without the need to clutter the HTML code itself with event handlers.

AJAX Support: The jQuery helps you a lot to develop a responsive and feature-rich site using AJAX technology.
Animations: The jQuery comes with plenty of built-in animation effects which you can use in your websites.
Lightweight: The jQuery is very lightweight library - about 19KB in size (Minified and gzipped).
Cross Browser Support: The jQuery has cross-browser support, and works well in IE 6.0+, FF 2.0+, Safari 3.0+, Chrome and Opera 9.0+
Latest Technology: The jQuery supports CSS3 selectors and basic XPath syntax.