jQuery is a JavaScript library that simplifies HTML document traversal, event handling, animating, and Ajax interactions. It allows developers to perform tasks like DOM manipulation more easily compared to vanilla JavaScript. While JavaScript can perform the same tasks, jQuery provides easy-to-use functions and flexibility. jQuery can be used with many programming languages on both the client-side and server-side. It has features for DOM selection, traversal, modification, events, CSS manipulation, effects/animations, Ajax, and extensibility. Learning the basics of jQuery takes about a week, but fully exploring its functions takes more time. The jQuery library is freely available on its official website.