Multi-family residential (also known as Multi-dwelling unit or MDU) is a categorization of housing where many separate housing units for residential (i.e. non-commercial) occupants are enclosed within one building or numerous buildings within one complex. A general form is an apartment building. Sometimes units in a multi-family residential building are condominiums, where usually the units are possessed independently instead of leased from a single apartment building possessor. Many deliberate groups of people include multi-family residences, such as in cohousing projects.