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 some API for entities connection, relationships and traversal.
Repositories form a layer which takes care about your entities. Repository requires a mapper as a dependency. Repository does not know anything about your storage (e.g. database), only manages entities and provides API for entities getting, filtering, storing and removing.
Everything is connected in central Model, which manages all repositories.