Housing unit

A housing unit is a house, apartment, group of rooms or a single room occupied as separate living quarters; that is,

• 1. When the occupants live separately from all other persons on the property
  AND
• 2. When there is direct access from the outside or through a common hall.

Also regard as a housing unit is a vacant room or group of rooms that are intended for occupancy as separate living quarters.
A housing unit may be occupied by a family or by a person living alone. It may also be occupied by two or more unrelated persons who share the living quarters.