Directives are one of the most important components of AngularJS application. They are extended HTML attributes. In other words, directives are something that introduces new syntax. They are markers on the DOM element which provides some special behavior to DOM elements and tell AngularJS’s HTML compiler to attach.
Their are many built in directives such as ng-model, ng-repeat, ng-show, ng-bind etc. All these directives provide special behavior to DOM elements. For example, ng-show directive conditionally shows an element, ng-click directive adds click events to the element; ng-app directive initializes an AngularJS application, etc.