What are directives in AngularJS?

Directives are markers on a DOM element (such as an attribute, element name, comment or CSS class) that tell AngularJS to attach a specified behavior to that DOM element or even transform the DOM element and its children. When AngularJS finds the directive at the time of rendering then it attaches the requested behavior to the DOM element. Angular comes with a set of these directives built-in, like ngBind, ngModel, and ngClass.