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

peer-to-peer
P2P
peer-to-peer network

    1. The kind of communication found in a system
   using layered protocols.  Each software or hardware
   component can be considered to communicate only with its
   peer in the same layer via the connection provided by the
   lower layers.

   (1994-12-14)

   2. A decentralised file sharing system like BitTorrent,
   Gnutella or Kazaa where computers that download data also
   store that data and serve it to other downloaders.  This
   increases the total bandwidth available in proportion to the
   number of users and so reduces download time.  It also
   improves resilience by providing multiple redundant sources
   for the same data.  This contrasts with client-server where
   all clients download the data from a single server (or
   mirror), sharing its fixed bandwidth.

   Peer-to-peer networks are typically ad-hoc and rely on users
   sharing the content they have downloaded for the benefit of
   other users.  Users who fail to do this are called "leaches".
   A "seed" is a node on a peer-to-peer network that is
   sharing a complete copy of a file, as opposed to other nodes
   that may only have some of the parts into which the file has
   been split.

   (2010-02-20)