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

ICMP
       Internet Control Message Protocol [version 4] (TCP/IP, RFC 792,
Internet)


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

Internet Control Message Protocol
ICMP

    (ICMP) An extension to the Internet Protocol (IP)
   that allows for the generation of error messages, test
   packets, and informational messages related to IP.  It is
   defined in STD 5, RFC 792.

   (1999-09-18)