noun
second floor; upstairs
Refers to the second story of a building or the upstairs area. In Japanese floor counting, the ground floor is 一階, so 二階 is one floor above ground level.
私の部屋は二階にあります。
My room is on the second floor.
二階から大きな音が聞こえた。
I heard a loud noise from upstairs.
Compound of 二 (two) and 階 (floor, storey). The reading にかい follows standard on'yomi for both characters.