Router outlets
The router-outlet is a directive that’s available from the @angular/router package and is used by the router to mark where in a template, a matched component should be inserted.
Thanks to the router outlet, your app will have multiple views/pages and the app template acts like a shell of your application. Any element, you add to the shell will be rendered in each view, only the part marked by the router outlet will be changed between views.
Visit the following resources to learn more: