The Collaborative International Dictionary of English v.0.48:

Compo \Com"po\, n.; pl. -pos.
   Short for Composition; -- used, esp. in England, colloq. in
   various trade applications; as :
   (a) A mortar made of sand and cement.
   (b) A carver's mixture of resin, whiting, and glue, used
       instead of plaster of Paris for ornamenting walls and
       cornices.
   (c) A composition for billiard balls.
   (d) A preparation of which printer's rollers are made.
   (e) A preparation used in currying leather.
   (f) Composition paid by a debtor.
       [Webster 1913 Suppl.]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

POS
       Piece Of Shit (slang, Usenet, IRC)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

POS
       Primary Operating System (OS, RCA Spectra 70)


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

POS
       Professional Operating System (OS, DEC), "P/OS"


V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

POS
       Programmable Object Select


The Free On-line Dictionary of Computing (30 December 2018):

POS

   point of sale