IGMP - membership report
An IGMP membership report is a message used by the IGMP protocol. It is the message that is sent by a host desiring to join a Multicast group. The term IGMP join message may also be used to describe the same message, but this is an informal term.
IGMP membership reports are used in both IGMPv2 and IGMPv3.
Links
https://networklessons.com/multicast/multicast-routing
https://forum.networklessons.com/t/multicast-routing/1330/41?u=lagapides