GECOS

When creating a new user account using the adduser program on Unix machines there is a field called GECOS that conventionally used to store information about the user, such as their real name or phone number.

adduser
    [options]
    [--home DIR]
    [--shell SHELL]
    [--no-create-home]
    [--uid ID]
    [--firstuid ID]
    [--lastuid ID]
    [--ingroup GROUP | --gid  ID]
    [--disabled-password]
    [--disabled-login]
    [--gecos GECOS]
    [--add_extra_groups]
    [--encrypt-home] user

--gecos GECOS
Set  the  gecos  field for the new entry generated.  adduser will not ask for finger
information if this option is given.

The cryptic title is not explained in the man pages. This field is called GECOS as it was originally used to describe the purpose of machines running the General Electric Comprehensive Operating System (GECOS), which had user accounts set up to access the services running on those machines, such as print spooling. This field was added to /etc/passwd, and was later repurposed to contain identifying information on each user. This anachronism has managed to persist into modern Unix and Linux system to this day.