The Great Houses of the Imperial Oferan Empire are enormous entities that are as big as many independant states. Whilst some date back to the founding of the First Empire 15,000-years ago and are descended from the 27 Tribes that existed before then most of them have been founded since, but all share one thing in common, they are all ruled by one family in the style of an heredity monarchy.
The Houses form a loose alliance called the Kuito of Great Houses, from which the 12 members of the Political Council are chosen to rule the Empire, with the elected Emperor chosen from these twelve. Only the Political Council has the ability to give the status of "Great" to a House and add them to the Kuito. There are about 150 Great Houses in the Kuito in the modern era.
A Great House is enormous, comprising of the Ruling Family and their various estates, etc, but also their businesses, schools and educations systems, fleets of civilians, transport, cargo and military ships and hardware, hospitals, factories, labratories, and support systems. They often have their own uplink channels and language, militaries and traditions.
Politics between Great Houses is full of intriege, with all Houses jockying for position and favour in order to gain enough votes for their Lord/ Lady to be placed on the Politicial Council. Sometimes feuds are solved by arranged marriages, at other times Houses go to war and fight until one is beaten or destroyed. If they are beaten then the beaten House enters into servitude of the victor, reclassified as a Slave House. They must then work their way back up to Servant House status.
A Great House can have hundreds of Servant Houses within it, either Houses that have volentarily joined them, or have been branched off from the ruling family over generations. These Servant Houses can be large themselves and sometimes grow big enough to earn or buy their freedom from the Great House and set up as an Independant House.