stairs
plural a set of steps that allow you to go from one level of a building to anotherThey heard footsteps on the stairs.
up/down the stairs: John raced down the stairs to answer the door.
the top/head of the stairs: Someone was waiting at the top of the stairs.
the bottom/foot of the stairs: He left his bags at the foot of the stairs.
a flight of stairs (=a set of stairs between two floors or levels): My bedroom was up two flights of stairs.
climb the stairs: I climbed the stairs to Charles’s office.