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

User Datagram Protocol
UDP

    (UDP) Internet standard network layer,
   transport layer and session layer protocols which
   provide simple but unreliable datagram services.  UDP is
   defined in STD 6, RFC 768.  It adds a checksum and
   additional process-to-process addressing information [to
   what?].  UDP is a connectionless protocol which, like TCP,
   is layered on top of IP.

   UDP neither guarantees delivery nor does it require a
   connection.  As a result it is lightweight and efficient, but
   all error processing and retransmission must be taken care of
   by the application program.

   Unix manual page: udp(4).

   [Postel, Jon, User Datagram Protocol, RFC 768, Network
   Information Center, SRI International, Menlo Park, Calif.,
   August 1980].

   (1998-02-11)