Source : Free On-Line Dictionary of Computing

Internet Group Management Protocol
     
         (IGMP) An extension to the {Internet Protocol},
        used by IP {hosts} to report their {host group} memberships to
        immediately-neighbouring {multicast} {routers}.
     
        See also {MBONE}.
     
        Version 1 of IGMP is defined in Appendix 1 of {RFC 1112}.
     
        Version 2 is proposed in {RFC 2236}.
     
        (1999-11-08)