garden apartment

So called since this form of housing is usually a cottage built in a home's back yard garden area.

garden apartment (plural garden apartments)

1. A detached mother-in-law apartment or cottage on the same parcel as the main house.
2. One of a set of low-rise apartment buildings built among landscaped grounds and often arranged around courtyards that are open at one end.

   a garden apartment complex

3. An urban apartment in a multistory building located at or below ground level.
   • 2003 August 15, Chuck Green, “Tenants are high on garden apartments”, in Chicago Tribune‎:

     "Because you're in the basement living in a garden apartment, when people are moving around upstairs, you can hear it. You wake up, look around, and realize it's someone above you," he said.

• in-law unit
• back house