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

point of presence

   (PoP) A site where there exists a collection of
   telecommunications equipment, usually modems, digital leased
   lines and multi-protocol routers.  An Internet access
   provider may operate several PoPs distributed throughout
   their area of operation to increase the chance that their
   subscribers will be able to reach one with a local telephone
   call.  The alternative is for them to use virtual PoPs
   (virtual points of presence) via some third party.

   (1994-12-13)