Resolved<P> says "if this is a promise, the type here is whatever the promise resolves to; otherwise, it's just the value"ReturnType<T> gets the return value of a given functionR['model'] (where R has to be Route itself or a subclass) uses TS's mapped types to say "the property named model on RModelFrom<Route> ends up giving you the resolved value returned from the model hook for a given route:model on the controllermodel on a Controller is always exactly the type returned by Route::model by writing something like this:model property will always stay in sync with the corresponding route’s model hook.model in either the afterModel or setupController hooks on the route! That's generally considered to be a bad practice anyway. If you do change the type there, you'll need to define the type in some other way and make sure your route's model is defined another way.