/ˈbækˌsaɪd/
NOUN
The rear part of the human body, particularly the buttocks or the area opposite the front of the torso.
The fleshy, rounded part of the human body on which a person sits, located below the lower back.
NOUN
The side or part of something that is opposite its front, or the area located behind its main or forward-facing side.
The part of an object, building, geographical feature, or area that is situated behind or opposite its front-facing side.