noun
Refers to the floor above the current one, or the upstairs area in general. Antonym: 階下 (かいか, downstairs).
Antonyms: 階下
階上の部屋から物音が聞こえる。
I can hear noises from the room upstairs.
noun
top of the stairs
Specifically the landing or area at the top of a staircase. Antonym: 階下 (かいか, bottom of the stairs).
Antonyms:
猫が階上で寝ている。
The cat is sleeping at the top of the stairs.