What are Angular directives, and how are they used in application development?

In Angular, a directive is a class that specifically attaches to DOM elements and modifies their behavior. There are three types of directives: *ngIf is structural; *ngFor is also structural because it changes the layout by adding or removing elements; ngClass is an example of an attribute directive because it modifies the element’s look or behavior. A component directive is effectively just defining a custom component. Directives make reusable components in an application, thereby allowing developers to place common behaviors in one place and reuse them throughout the app.