jQuery is a very useful library for client side development but it doesn’t provide any mechanism of how to manage your JS code/files etc. There are many other JS libraries.
AngularJS (commonly referred to as “Angular” or “Angular.js”) is a complete JavaScript-based open-source front-end web application framework mainly maintained by Google and by a community of individuals and corporations to address many of the challenges encountered in developing single-page applications. [Ref: Wikipedia]
AngularJS is the frontend part of the MEAN stack.