building
A structure primarily intended to shelter occupants, usually enclosed but including related open forms.
A building is a general class of structures which consists mostly of constructions which shelter their occupants. Most buildings are enclosed spaces, but a building may also be open to the air. Certain types of buildings may deviate from these guidelines, being classified as buildings because of their general relation to structural forms which are usually buildings.
Sheltering occupants is the usual organizing purpose, although enclosure is not an absolute requirement. Some related structural forms share that building identity while remaining open to the air.
A building's physical form and its current usage describe different aspects of the object. A change in occupants or activity does not by itself alter the built form.