A group is a collection of several projects.
If you organize your projects under a group, it works like a folder.
You can manage your group member’s permissions and access to each project in the group.
GZ Pub
Apparently GitLab doesn't let you create a Public repository in a group that is Private. I understand what they are thinking, but I disagree. Unfortunately I'm not going to waste my time to fork and maintain my own version of GitLab.