IRC is used by Electrum server to find 'peers' - other Electrum servers. The current list can be seen by running:
./server.py peers
The following config file options are used by the IRC part of Electrum server:
[server]
irc = yes
host = fqdn.host.name.tld
ircname = some short description
'irc' is used to determine whether the IRC thread will be started or the Electrum server will run in private mode. In private mode, ./server.py peers will always return an empty list.
'host' is a fqdn of your Electrum server. It is used both when binding the listener for incoming client connections, and also as part of the realname field in IRC (see below).