Wiktionary
back end
n. 1 The rear, back, or invisible portion (of something). 2 (context computing English) that part of a hardware or software system that is farthest from the user; the internals rather than the user interface. 3 (context UK dialectal Northern England Scotland English) The latter end of any given time, especially the latter part of the year; autumn; late autumn.
WordNet
Usage examples of "back end".
Sir Grummore, unbuttoning the back end and standing up to mop his brow.