self-storage unit; rental storage room
A rented storage space, often in a dedicated facility, for personal or business items. The term is a wasei-eigo from English 'trunk room'.
from English trunk room
I stored my belongings in a self-storage unit during the move.
Rare usage; normally expressed as トランク. This sense is a direct borrowing from English 'trunk' and is not the primary meaning of トランクルーム.
See also: トランク
In old catalogs, you may see the expression トランクルーム for a car's trunk.