The word generally describes the nature and behavior of the social controlling group. Tyranny is a term which refers to different forms of oppression, either by government, or by a social situation in which a group is tyrannized by others. It invariably involves suppression of dissent and opposition, and use of the system of law to support the oppressor. Tyranny is commonly associated with dictatorships, but this isn't necessarily the case. Military juntas, theocracies and other forms of government have been known to conduct systematic oppression of people under their control.
Examples of Tyranny:
The French Terror
Khmer Rouge government of 'Kampuchea'/ Cambodia