What are the various roles supported by the Group module?
Here is a summary of the various roles used by the Group module:


Configured Global Roles: These roles can be configured via the admin interface of the Group module, they are available (to grant permissions) for all individual groups (regardless of the "Group Type"). These roles cannot have permissions that vary per group type (they are all the same). Typical examples of such roles could be "Group Moderator" or "Group Administrator".
Special Global Roles: These are the special (hardcoded) roles named "Outsider" (= a signed in user that did not join a group) and "Member"  (= a signed in user that did join a group). These cannot be defined by the Drupal administrator, and they are always available for any group. Unlike Configured Global Roles, these roles can have different permissions sets for each group type. Special case: the role "Anonymous" is related to a user that is not signed). 
Group Specific Roles: These roles can be configured per group type and will only be available on groups of that group type. As an example, for a group type like "Class", you could configure roles such as "Teacher" and "Student".