N.Y.C. Admin. Code § 28-305.4.1: § 28-305.4.1 Definition.

As used in this article, the following term shall have the following meaning:

RETAINING WALL. A wall that resists lateral pressures and limits lateral displacement caused by soil, rock, water or other materials, except that basement and vault walls that are part of a building, underground structures, including but not limited to utility vault structures, tunnels, transit stations and swimming pools, shall not be considered retaining walls.