Which file contains information about secondary groups on the system?

The file that contains information about secondary groups on the system is /etc/group. This file defines the group names, group IDs, group passwords, and group members for each group on the system. The primary group information for each user is stored in /etc/passwd file. References:https://documentation.suse.com/sles/15-SP3/html/SLES-all/sec-user-group.html#sec-user-group-files