back end

The rear, back, or unseen portion (of something).

That part of a hardware or software system that is farthest from the user; the internals rather than the user interface.

The latter end of any given time, especially the latter part of the year; autumn; late autumn.

Money paid on a contingent deferred basis, for example, as a proportion of the profits or revenue of a work.

The processing of spent fuel from a nuclear reactor into reusable materials.