Components are a clean way of organizing UI code into self-contained, reusable chunks, which contain their own view and logic. Components can be composed together to create a complex user interface. Components can optionally receive properties from the outside world and optionally communicate through callbacks or events. The business logic, structure and styling can be encapsulated inside the component code.
Components in Angular 2 are just directives with a view. Actually, the component in Angular 2 is a type of directive. We can also write a directive that doesn't include a template (and will not be called component) in Angular 2.
Those directives are very similar to the directives you're familiar with in Angular 1.x. The main difference is that in Angular 2.0 we think of two kinds of directives: attribute directives that add behavior to the elements, and structural directives which we named: components.