This setting has 3 options:

* No groups - There are no sub groups, everyone is part of one big community
* Separate groups - Each group member can only see their own group, others are invisible
* Visible groups - Each group member works in their own group, but can also see other groups

The group mode defined at course level is the default mode for all activities within the course. Each activity that supports groups can also define its own group mode, though if the group mode is forced at course level, the group mode setting for each activity is ignored.