noun
storage closet; shed
Refers to a dedicated storage space or small building for keeping items; can be a closet, cupboard, or outdoor shed.
庭に収納庫を置いて、園芸道具をしまっている。
I keep a storage shed in the garden and put away gardening tools.
この収納庫には季節の衣類が入っています。
Seasonal clothes are kept in this storage closet.
クローゼット is a loanword for a clothes closet, whereas 収納庫 can refer to any storage closet or shed, not limited to clothing.
Compound of 収納 (storage) + 庫 (warehouse, storehouse).