Orm is clearly designed to abstract entities from database implementation, therefore it separates your model into three basic layers:
Entities are data crates, hold your data, validate values and provide API for value encapsulation, e.g. for relationships.
Repositories form a layer which takes care about your entities. Repositories manage entities and provide an API for thier retreiving, filtering and persiting.
Everything is connected in the central Model. Each entity must have defined own repository and mapper.