IRCd

An IRCd, meaning Internet Relay Chat server program, is a program, server software that uses the IRC protocol. This allows people to talk to each other on the Internet. They exchange textual messages in real time.
The server accepts connections from IRC clients on a group of TCP ports. When the server is part of an IRC network, it also keeps one or more connections with other servers/daemons.
The word "ircd" once referred to only one piece of software.