jQuery is a new kind of JavaScript library that makes it easier for designers to control HTML events, animations, and other interactions on a web page by adding and removing style sheet handlers. These handlers are either HTML classes or IDs; the handlers are specified in a style sheet, which then tells the browser how to position and style HTML elements. With jQuery, web designers can quickly and easily write these handlers to the document on specified events, such as a mouse click or a hover, and when we do so, it will change the style and/or position of that element. jQuery also simplifies AJAX--the client-side web development techniques for creating interactive web applications. AJAX applications can retrieve data from the server quietly in the background without interfering with how a web page displays or behaves. AJAX uses HTML and CSS (cascading style sheets) to change style and layout via user interaction and input.