The rear, back, or unseen portion (of something).
The processing of spent fuel from a nuclear reactor into reusable materials.
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 bottom; the buttocks or anus.
Foundation.
The underlying basis or principle for a theoretical or mathematical system.