It is typically used to record general information about the account or its user(s) such as their real name and phone number.
The typical format for the GECOS field is a comma-delimited list[1][2] with this order: In most UNIX systems non-root users can change their own information using the chfn or chsh command.
Some early Unix systems at Bell Labs used GECOS machines for print spooling and various other services,[3] so this field was added to carry information on a user's GECOS identity.
IRC clients are able to supply this field when connecting.
Hexchat, an X-Chat fork, defaults to 'realname', TalkSoup.app on GNUstep defaults to 'David Okeamah', and irssi reads the operating system user's full name, replacing it with 'unknown' if not defined.