IRC - Stands for Internet Relay Chat is an internet based chat protocol. Main idea is to have users connect to a server network, where they can then send messages to each other through channels or direct chat
XMPP (Extensible Messaging and Presence Protocol) is an open, standard protocol for near-real-time exchange of XML-structured data.
"Regardless the irc protocol is more simplistic in nature can handle orders of magnitude more client connections than xmpp for the same memory utilization uses less bandwidth on the wire doesn t require authentication although you can add this feature etc"
from question "What's the best open protocol for chat room software?"