Setback

In New York usage, a setback is the horizontal step a building takes as it rises: the point where the street wall stops and the upper floors retreat from the street line, whether to stay under a sky exposure plane in non-contextual districts or to satisfy the prescribed base-height and setback rules of contextual districts. The device preserves light and air at the sidewalk while letting height continue further back on the lot.

Setbacks are distinct from yards — the ground-level open areas required along lot lines — though both shrink the buildable envelope. Together with height limits and coverage rules, setback requirements are why a lot's floor-area budget cannot simply be extruded upward: the shape of the allowable volume, not just its size, is regulated.