Y - A Y-shaped plumbing fitting.
Zone - The section of a building that is served by one heating or cooling loop because it has noticeably distinct heating or cooling needs.
Zone valve - A device, usually placed near the heater or cooler, which controls the flow of water or steam to parts of the building; it is controlled by a zone thermostat.
Zoning - Ordinances regulating the ways in which a property may be used in any given neighborhood. Zoning laws may limit where you can locate a structure. Also see building codes.