The word "tenement" originally applied to any building occupied by three or more families, the tenants. The term has since become applied to such buildings of a lower standard, generally overcrowded, and in contrast to "apartments" or "blocks of flats."
The worst living conditions were in cellars, and the first legislation on tenements required that a cellar unit extend at least a foot above ground level. Cellar dwelling declined in the latter part of the 19th century.
Tenements could be either conversions from previously middle-class homes, sometimes called "rookeries," or buildings constructed for the specific purpose. They were unpleasant places to live, had inadequate sanitation, and posed a fire danger.
New York City reacted to an expose` of tenement living by Jacob Riis in 1890 with legislation, culminating in a law in 1903 that required expanded open space as well as sanitary facilities in every unit.