Each occupant receives an undivided interest in the ownership of the apartment he uses and a common interest in all other facilities. This is usually effected by forming a corporation with each owner receiving stock in the corporation equal to his investment. The form of ownership is shares/stock in a corporation. The corporation owns the real estate.

a unit in a building owned by a corporation

A cooperative is a corporation which holds title to the land and building. Each coop owner has shares of stock in the corporation, which corresponds to an equivalent proprietary lease of his apartment space. Coops were popular in New York City at one time, but are now less common because of their lack of marketability due to high association fees.