A brown dwarf was a type of star that was in the process of a formation. Their mass was too small to maintain hydrogen fusion reaction and they were sometimes considered to be large gas giants.
By the time of the Galactic Civil War, the sector of space that separated the planets Kupoh and Gamorr was largely unexplored, and Luke Skywalker suspected it might contain uncharted brown dwarfs that could become a hazard for hyperspace travel. Doornik-1142 was a brown dwarf star.