Calendar Permissions 
Calendar permissions follow forum permissions in that inheritance and multiple group membership are supported. In simplest terms, this means that a user can belong to multiple groups at once which gives them the combined permissions of all of their groups. There are also global calendar permissions specifiable at the usergroup level (Usergroups->Usergroup Manager->Edit->Calendar Permissions). You can then override any usergroup permission for a specific calendar by creating custom permissions for just this calendar.

Please refer to the Usergroup Permissions' section if you need further clarification on what is meant by inheritance and multiple group membership.
User Contributed Notes: Calendar Permissions Add a Comment