Groups are typically used to isolate bugs that should only be seen by certain people. Group permissions are such that if a bug belongs to a group, only members of that group can see the bug. Most of the functionality of groups and group security is controlled at the product level. For more information on the parameters that control group behavior globally, see Group Security. To create a new group, choose a regular expression that will automatically add any matching users to the group, and choose an icon that will help identify user comments for the group.”]
Source: https://bugzilla.readthedocs.io/en/5.0/administering/groups.html