jQuery is a Javascript library that simplifies the management of an HTML document: navigation, event handling, animations, Ajax interactions for web development etc. The purpose of this library is to change (well) the way Javascript interacts and leaves its mark on our work.
A concrete example of an application that uses this technology is the slider on the main page, where the last articles are changed at a interval of less than one second each. There is nothing to say when we can say, that the same effects are obtained with javascript, but it will probably take "little" to make such an implementation.