jQuery is a fast and concise JavaScript Library that simplifies HTML document traversing, event handling, animating, and Ajax interactions for rapid web development. jQuery is designed to change the way that you write JavaScript.

Features

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

Source: jQuery & Wikipedia