What is a decorator in Angular 2?

Decorators are functions that are invoked with a prefixed @ symbol and immediately succeeded by a class, parameter, method or property. The decorator function is supplied data about the class, parameter or method, and the decorator function returns something in its place or manipulates its target in some way. Usually, the "something" a decorator returns is the same thing that was passed in, but it has been augmented in some way.

Decorators are designed for a future version of JavaScript, but the Angular team wanted to use them, and they have been included in TypeScript.