The Wohnungsgeber (the “apartment-giver”) is the person who gives you a room or an apartment to rent. It can be the landlord, or the main tenant (Hauptmieter).1 The main tenant must get permission from the landlord to sublet a room or the entire apartment. In some situations, the landlord can refuse.2
Only the Wohnungsgeber can sign the Wohnungsgeberbestätigung. You need this document to register your address in Germany.