NOT FRONT › the part of something that is furthest from the front or in the opposite direction to the front: He wrote his number down on the back of an envelope. We were sitting near the back and couldn't see much. I always keep a blanket in the back of the car.
BODY › the part of your body from your shoulders to your bottom: back injuries/pain He was lying on his back.
SEAT › the part of a seat that you lean against when you are sitting: the back of a chair
back to front UK › with the back part of something where the front should be: You've got your trousers on back to front.
in back of US › behind: They sat in back of us on the plane. → See also a pat on the back → See also be (like) water off a duck's back