The Unknown Regions, also referred to as Unknown Space, the Unknown Territories, the Unknowns, and the Outer Reaches, was a region of the galaxy located in the galactic west beyond the Outer Rim. Largely unexplored throughout galactic history, it remained a mystery to space travelers and served as a source of tales and wonders.
To those who lived in the Unknown Regions, it was known as the Chaos. They knew the rest of the galaxy as «Lesser Space.» The Chaos was a very dangerous place to navigate due to supernovae, black holes, gravity wells, and stranger phenomena. These hazards made navigation computers unreliable within the Chaos, and were the source of the name «Chaos.» Due to such hazards, the peoples of the Unknown Regions employed Force-sensitive navigators, individuals endowed with the Force power of precognition, to navigate. When navigators were unavailable, long hyperspace journeys had to be jump-by-jump instead.
The Unknown Regions were originally introduced in the Heir to the Empire Sourcebook, which was an accompaniment to the Legends novel Heir to the Empire. It was brought into canon when the planet Ilum was introduced in the Star Wars: The Clone Wars episode «The Gathering.»
Pablo Hidalgo explained in Rebels Recon that the borders of the Unknown Regions were known (and therefore should be visible on the map of the galaxy) but what were within the regions were unknown. This is in contrast with Wild Space, which was outside the known map of the galaxy (in other words, «off the edge of the map»).