lean-to         
noun [ C ] uk/ˈliːn.tuː/ us/ˈliːn.tuː/
 (依附在大建筑侧面的)小屋,偏房,侧房
a building joined to one of the sides of a larger building with which it shares one wall
  a house with a lean-to garage 带车库的别墅 
  US(供宿营用的)斜顶简易房 
a shelter or simple building with a roof that slopes in one direction, used for sleeping in outside