RHEL 8, RH124, Chapter 6, Section 1, What is a Group?
In the explanation of /etc/group, it says this for field two:
Obsolete group password field. This field should always be x.
In my humble opinion, the course content frequently over-explains things. In this case, it side-stepped an explanation altogether.
Sure, I've never used a group password -- and I've never seen one used. That, however, does not mean that it is never used (one definition of "obsolete"). In fact, the gpasswd command still exists. As result, a group password could be used.
I'd suggest that an explanation, like the one used for field two for /etc/passwd, could be used with a little modification:
The group's password used to be stored here in encrypted format. That has been moved to the /etc/gshadow file (which is beyond the scope of this lesson). This field should always be x.
Program Lead at Arizona's first Red Hat Academy, est. 2005 Estrella Mountain Community College