Most of the websites and web-applications are developing in server scripting languages. And the GUI part are designed in jquery, css and html. For GUI designing purpose jquery is easy and light so that the website will open quickly.
We use jquery because it is the cross browser compatible, so that the GUI remain same in the modern browsers. Jquery also using to send back-end or to gathering the data from cross domain. In this example we use jquery for dynamic dependent select boxes so that the page will not refresh every time when the related data are loading.