It is typically used to record general information about the account or its user(s) such as their real name and phone number.
GECOS means General Electric Comprehensive Operating System, which has been renamed to GCOS when GE’s large systems division was sold to Honeywell.
- User's full name (or application name, if the account is for a program)
- Building and room number or contact person
- Office telephone number
- Any other contact information (pager number, fax, etc.)
In most UNIX systems normal users can change their own information using the chfn or chsh command.