AngularJS is an open-source web application framework that enhances HTML with new attributes, facilitating the development of single-page applications. It follows the MVC architecture, enabling a clean separation between data (model), user interface (view), and business logic (controller), while providing features such as data binding, templates, and services. Key directives like ng-model, ng-repeat, and ng-controller help in application development, and built-in filters allow for data formatting.