noun

• (chiefly Canada, US, Australia, Philippines) A complete domicile occupying only part of a building, especially one for rent; a flat.
  "apartment dwellers"
• (archaic) A suite of rooms within a domicile, designated for a specific person or persons and including a bedroom.
  "By this contrivance I got into the inmost court; and, lying down upon my side, I applied my face to the windows of the middle stories, which were left open on purpose, and discovered the most splendid apartments that can be imagined. There I saw the empress and the young princes in their several lodgings, with their chief attendants about them."
• (obsolete) A division of an enclosure that is separate from others; a compartment.
  "1883 April 23, Slawson v. Grand Street R. Co., 107 U.S. 649, 2 S.Ct. 663, 664, The specification described the ordinary fare-box used in street cars and omnibuses, consisting of two apartments, the one directly above the other.... [T]he passenger deposited his fare in an aperture in the top of the upper apartment. It fell upon and was arrested by a movable platform.... This platform turned on an axis acted on by a lever. When turned, the fare fell into the lower apartment, which was a receptacle for holding the fares accumulated...."
• (computing, COM) A conceptual space used for separation in the threading architecture. Objects in one apartment cannot directly access those in another, but must use a proxy.