A House in the Dune Universe refer to dynastic seat of power, sometimes limited to a single world and sometimes spanning several worlds. Numerous Houses existed within the hierarchy of the Imperium. Collectively they formed the landsraad, which was governed by the High Council. Houses could be differentiated into Houses Major and Houses Minor.
Each House usually maintained their base of operations on a specific planet - typically their ancestral home. Banished Houses were exiled to Tupile. Banishment was usually decreed by the Emperor, or by a ruling of the Landsraad. This would usually occur because the House in question did not follow the Great Convention, for example, employing atomics against peoples.
Not surprisingly, some Houses possessed more power and influence than others. Some possessed enough power to rule entire planets. These were known as Great Houses, Major Houses, or Families. It was from one of these Houses that control of the Imperium, the realm of the Known Universe, was maintained. For more than 10,000 Standard Years, the Imperium was ruled by House Corrino.
As a consequence of this framework, there was constant plotting between Houses, and on occasion two or more Houses would form an alliance to thwart or destroy a mutually rival House.