The riddle
What Goes Up and Down but Never Moves?
Going nowhere
Stairs lead upward and downward, and they stay exactly where they are. "Goes" describes the route a person takes along them, not any motion of the stairs themselves. A staircase, a flight of steps and "the stairs" are the same answer. An escalator does not fit, because its steps really do move.
The parts of a stair
Each step has two parts. The tread is the flat surface a foot lands on, and the riser is the upright piece between one tread and the next. The long slanted boards that carry them are called stringers. The rail along the side is the banister, and the upright posts that hold it up are balusters. Merriam-Webster gives these meanings for all five words.
How tall a step may be
In American home building, the International Residential Code sets a maximum riser height of 7 3/4 inches and a minimum tread depth of 10 inches, though local rules can differ. That limit decides how many steps a house needs. A floor-to-floor height of 9 feet is 108 inches, and 108 divided by 7 3/4 is just under 14, so the flight needs at least 14 risers.
A bit of arithmetic to share
Counting the steps on the nearest staircase and dividing the height between the floors by that number gives the real riser height, which is a good way to check a home against the limit above.