mother-in-law suite       
noun [ C ] US uk/ˈmʌð.ə.rɪn.lɔː ˌswiːt/ us/ˈmʌð.ɚ.ɪn.lɑː ˌswiːt/ (also mother-in-law apartment, in-law suite, in-law apartment); (UK granny flat)
 在房子里或住处附近置备的独立居所,用于安置年长父母,老太太套间
a separate living space in or close to a larger home where an elderly (= older) parent, or elderly parents, can live
  In five years of renting out our furnished mother-in-law suite, we have only had one month with no renter. 我们把配了家具的老人套房租出去,五年里只有一个月没有租客。 
 A mother-in-law apartment can be in a separate structure on the same lot, such as above a garage, or a freestanding structure of its own.  老人套房既可以是同一块地基上的独立居室,比如建在车库顶上,又可以是自带地基的独立结构。 
 - More examples
 - Adding a mother-in-law suite to your property may increase its value by a significant margin.
 - This home features two full mother-in-law suites with individual kitchens.
 - He moved in last February after renovations, keeping the upstairs as the workspace and his own quarters in the basement's mother-in-law apartment.