Stair angle and pitch
Degrees, ratio and percentage slope — and whether that pitch is comfortable or even legal.
What the bands mean
30–37° is the comfortable range for a stair in daily use. Below 30° a stair starts to eat floor space for little gain; above about 42° it stops being a stair in the eyes of UK Part K, which caps a private stair there.
Pitch is a consequence, not an input. It falls out of the riser and going you chose, which is why the stair calculator is usually the better place to start.