Rear yard

The rear yard is required open area along a lot's rear lot line, and it is the most persistent yard obligation in the residence-district rules: districts that long ago abandoned front and side yards still require open ground at the rear. Lot by lot, paired rear yards meeting across rear lot lines form the continuous open seam running down the middle of New York's blocks — a shared light-and-air corridor the whole block's windows depend on.

Corner lots are treated differently, having no rear lot line in the ordinary sense, and through lots substitute an equivalent open area mid-lot. Rear-yard encroachments are a classic enforcement and legalization issue, because an extension too deep bites into a resource that is collective by design.