What are Event emitters in Angular 2 ?

In simple words, event emitters are used to send a data or message from child component to parent component.

EventEmitter is an angular2 abstraction and its only purpose is to emit events in components. Quoting a comment from Rob Wormald [...] EventEmitter is really an Angular abstraction and should be used pretty much only for emitting custom Events in components. Otherwise, just use Rx as if it was any other library. This is stated really clear in EventEmitter's documentation. Use by directives and components to emit custom Events.

https://dzone.com/articles/understanding-output-and-eventemitter-in-angular