A room or floor below ground level in a building. In Japanese homes, a 地下室 is often used for storage, a hobby room, or a home theater, while in commercial buildings it may house parking or machinery.
This house has a spacious basement.
We store the wine in the cellar.
My father went down to the basement to get some wine.
We're planning to build a basement in the new house.
When the earthquake hit, everyone hid in the basement.
The culprit locked the victim in the basement.