HTML is great for declaring static documents, but it falters when we try to use it for declaring dynamic views in web-applications. Angular lets you extend HTML vocabulary for your application. The resulting environment is extraordinarily expressive, readable, and quick to develop. Angular is built on the belief that declarative programming should be used to create user interfaces and connect software components, while imperative programming is better suited to defining an application's business logic.
The framework adapts and extends traditional HTML to present dynamic content through two-way data-binding that allows for the automatic synchronization of models and views. As a result, AngularJS de-emphasizes explicit DOM manipulation with the goal of improving testability and performance. Read more about Angular here: Angular.org