It's a framework to build ambitious web applications. It's a client side framework meaning that it runs in a web browser. That means the application does not have to reload a full page, it can just fetch data it needs and update only components that have to be re-rendered. It's a opinionated framework meaning that instead of configuring it you follow already set conventions. This means that when you'll understand one application written in Ember, you'll be able to jump into another app and find your way very quickly.