It is the automatic synchronization of data between model, view components.
Objects that refer to the model. They act as a glue between controller, view.
AngularJS come with several built-in services for example $http to make a XMLHttpRequests. Singleton objects which are instantiated only once in app.
These select a subset of items from an array, returns a new array.
Directives are markers on DOM elements (such as elements, attributes, css, and more). Used to create custom HTML tags that serve as new, custom widgets. AngularJS has built-in directives (ngBind, ngModel…)