The guest room key is the key given to the guest to open the lock of their assigned room. It is typically provided at check-in.
- Emergency key is a key used by staff in case of emergencies but does not open individual guest rooms.
- Master key is used by hotel management or staff to access all rooms in the hotel but is not given to guests.
- Card key is a modern electronic key used to open guest room locks, and it serves the same purpose as a traditional room key. However, the specific answer depends on the type of hotel.
Thus, the correct answer is Guest room key.