The term the Known Universe referred to the area of the universe that was explored and documented by humans. The vast majority of this space was claimed to be within the realm of the Padishah Emperors, who referred to themselves as Emperors of the Known Universe.
Though the emperors laid claim to ruling the known universe, in reality it was considered to be greater than the size of the Imperium itself. During the reign of Leto II, the Tleilaxu sought to establish colonies outside of Leto's empire, but still within the known universe. The Tleilaxu believed that Leto's prescience ended at the borders of the Imperium. They were incorrect, as Leto came to demonstrate.
The size of the known universe increased sporadically over history. The most significant growth in the universe charted by humankind came at two specific points:
Behind the ScenesEdit
Even after the merger of the Bene Gesserit and the Honored Matres, when the known universe was larger than it had ever been, the full extent of manned space is undisclosed. It is, however, acknowledged as being far larger than any group can fathom, and encompasses multiple galaxies, thanks to the power of space folding.