Computed Properties and @each

I've been reading through the docs and API and I'm having a hard time finding an explanation for the following:

export default Ember.Controller.extend({
  collectionTotal: function() {
    var games = this.get('model');
    return games.length
  }.property('@each')
});

What is actually happening with the .property('@each')? I know I am getting the computed property back, I don't understand what @each is.