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

protocol stack

    A layered set of protocols which work together to
   provide a set of network functions.  Each intermediate
   protocol layer uses the layer below it to provide a service
   to the layer above.

   The OSI seven layer model is an attempt to provide a
   standard framework within which to describe protocol stacks.

   (1997-12-07)