The mappings of GID and group names are in the file /etc/group.

• First field, group name.
• The second field is the encrypted password.
• Third field, “GID
• The fourth field is the list of users belonging to that group, separated by commas.

https://docs.freebsd.org/en/books/handbook/basics/

Taken from UCH Wiki. https://wiki.ulascemh.com/doku.php?id=en:cs:op:bsd:chmod