Linux Pocket Guide, 2nd Edition

Instant Messaging

pidgin	Instant messaging and IRC client.
talk	Linux/Unix chat program.
write	Send messages to a terminal.
mesg	Prohibit talk and write.
tty	Print your terminal device name.

Linux provides various ways to send messages to other users on the same machine or elsewhere on the Internet. These range from the ancient programs talk and write, which work over Linux terminal devices (ttys), to more modern instant messaging clients like pidgin.