AngularJS is a JavaScript framework for building web applications. It was developed and is maintained by Google. Some of the key features and concepts of AngularJS include:

Two-way data binding: AngularJS allows developers to easily keep the view and the model in sync by automatically updating the view when the model changes and updating the model when the view changes.

Directives: AngularJS allows developers to extend HTML with custom tags and attributes, called directives. Directives can be used to create reusable UI components, such as form inputs, and can also be used to manipulate the DOM.

Templates: AngularJS uses templates to describe the structure of a component's UI. Templates are written in HTML and can include expressions, directives, and other AngularJS-specific elements.

Services: AngularJS provides a way to create reusable services that can be injected into components. Services can be used to encapsulate logic and share data across multiple components.

Dependency injection: AngularJS uses a dependency injection (DI) system that allows developers to easily manage the dependencies of their components. This can be used to simplify the process of wiring up dependencies and make it easier to test components.

Routing: AngularJS provides a powerful routing system that allows developers to easily handle client-side navigation. This can be used to create Single Page Applications (SPAs) that can load different views based on the current URL.

Testing: AngularJS provides a testing framework and tools that make it easy to test the different parts of an AngularJS application, such as components, services, and directives.