Two-way data binding - It is used to synchronize the data between model and view. It means, any change in model will update the view and vice versa. ng-model directive is used for two-way data binding.

One-way data binding - This binding is introduced in Angular 1.3. An expression that starts with double colon (::), is considered a one-time expression i.e. one-way binding.

AngularJS handle data-binding mechanism with the help of three powerful functions: $watch(), $digest() and $apply(). Most of the time AngularJS will call the $scope.$watch() and $scope.$digest() functions for you, but in some cases you may have to call these functions yourself to update new values.

AngularJS is a MVC framework. It does not implement MVC in the traditional way, but rather something closer to MVVM Model-View-ViewModel).

Models are plain old JavaScript objects that represent data used by your app. Models are also used to represent your app's current state.

A viewmodel is an object that provides specific data and methods to maintain specific views. Basically, it is a $scope object which lives within your AngularJS app's controller. A viewmodel is associated with a HTML element with the ng-model and ng-bind directives.