A setback, sometimes called step-back, is a step-like recession in a wall

Wall

A wall is a usually solid structure that defines and sometimes protects an area. Most commonly, a wall delineates a building and supports its superstructure, separates space in buildings into rooms, or protects or delineates a space in the open air...

. Setbacks were initially used for structural reasons, but now are often mandated by land use codes.
Setbacks were used by ancient builders to increase the height of masonry

Masonry

Masonry is the building of structures from individual units laid in and bound together by mortar; the term masonry can also refer to the units themselves. The common materials of masonry construction are brick, stone, marble, granite, travertine, limestone; concrete block, glass block, stucco, and...

 structures by distributing gravity loads produced by the building material such as clay, stone or brick. This was achieved by regularly reducing the footprint of each level located successively farther from the ground.