/ˈbækˌsaɪdz/
NOUN
The fleshy rear part of the human body, particularly the buttocks or the area on which a person sits.
The rounded, fleshy parts of the body below the lower back that support a person when sitting.
NOUN
The side or part of an object that is opposite its front, or the reverse side of something.
The part of an object, structure, or place that is located behind or opposite its front-facing side.