Group policies are used to allow or deny certain permissions to a user or a group of users.
Group Policy Objects can only be assigned to an Active Directory Site, Domain or an OU. A group policy object cannot be assigned to a group. A workaround for this would be to place the group in an OU and then assign permissions to that OU. Because of the Heirarchical nature of the Active Directory objects, all objects that exist in that OU will inherit those permisisons.
Again, the three levels where you can apply Group Policy Objects (Permissions) are as given below:
1. Site Level
2. Domain Level
3. OU Level
OU (Organizational Unit): An OU is an Active Directory Container Object. It can contain Sub-OUs, Users and Groups.