Certain words used in this act shall be defined, for the purposes thereof, as follows:

“Tenement house” is any house or building, or portion thereof, which is: (a) intended or designated to be occupied, or (b) leased for occupation, or (c) actually occupied, as a home or residence for three or more families, living in separate apartments, and doing their cooking upon the premises.

“Apartment” is a room or suite of two or more rooms, occupied or leased for occupation, or intended or designed to be occupied, as a family domicile.

“Basement” is a story partly, but not more than one-half,--“cellar” is a story more than one-half,--below the level of the street or ground adjacent to or adjoining the same; where the grade of a street adjacent to, or of ground surrounding, a tenement house varies, the mean or average grade of such street or ground shall be regarded as the grade of such street or ground, in the meaning of this act.