For purposes of this article, the following definitions shall apply:
A residential rental unit which is:
A residential rental unit for which no certificate of occupancy has been issued;
A residential rental unit which is in excess of the number of such units for a particular building or zone according to this chapter; or
A residential rental unit which was created without the required plumbing, electrical or building permits.
A building, or portion thereof, rented or offered for rent for dwelling purposes to one or more tenants or family units.