后 (hòu) — behind; back (in space); after; later (in time)

后 is a bound morpheme meaning 'behind' or 'after,' used to build compounds like 后面/以后. 背 is its physical-body counterpart (the back of a person).

Two or more meaningful parts placed together so that their meanings combine into a new one.

This origin belongs to the traditional form 後; 后 is its simplified writing.

The traditional form 後 showed 夊 (foot) bound by 幺 (thread), a foot caught by a rope and lagging behind; the simplified 后 is a later abbreviation, and 后 also has a different meaning.