back end vs tail end

back end

noun
  • 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. 

tail end

noun
  • The hindmost part of anything (a person, animal, or object), the rear end; the butt, buttocks; hindquarters, rump. 

  • The last part of a period of time, event, or situation; the concluding or final part. 

How often have the words back end and tail end occurred in a corpus of books? (source: Google Ngram Viewer )