erc-message
erc-message is a compiled Lisp function in `erc-backend.el
'.(erc-message MESSAGE-COMMAND LINE &optional FORCE)
Send LINE to the server as a privmsg or a notice.
MESSAGE-COMMAND should be either "PRIVMSG" or "NOTICE".
If the target is ",", the last person you've got a message from will
be used. If the target is ".", the last person you've sent a message
to will be used.