What is Yard?
A yard is a required open area along the lot lines of a zoning lot which must be unobstructed from the lowest level to the sky, except for certain permitted obstructions. Yard regulations ensure light and air between structures.
A front yard* extends along the full width of a front lot line. In the case of a corner lot, any yard extending along the full length of a street line is considered a front yard. (See also Setbacks, Front Yard or Ground Level)
A rear yard* extends for the full width of a rear lot line. In residential districts, the minimum depth of a rear yard is 30 feet, except in R2X districts. In commercial, manufacturing and R2X districts, the minimum depth of a rear yard is 20 feet. A corner lot is not required to have a rear yard. In commercial and manufacturing districts, and for some community facility buildings in residence districts, the rear yard may be occupied entirely by a single-story building up to a height of 23 feet.
A side yard* extends along a side lot line from the required front yard, or from the front lot line if no front yard is required, to the required rear yard, or to the rear lot line if no rear yard is required. In the case of a corner lot, any yard that is not a front yard is considered a side yard.
reference: Glossary of Planning Terms – NYC Planning