storage space above closet; upper cabinet
Refers to a small storage compartment built above a closet or alcove, often found in traditional Japanese rooms.
天袋に布団をしまっておく。
I keep the futon in the storage space above the closet.
Compound of 天 (ten, 'ceiling') and 袋 (fukuro, 'bag'), referring to a bag-like storage space near the ceiling.