Jotun is a fringe colony.
In 2502 the War Pigs kidnapped a woman, Ellen Houston, from the mobile mine of Revelation, killing some of their security forces as they left. They had done so at the behest of her (ex-)husband, Denny.
During the development of StarCraft II: Wings of Liberty, Jotun was the location of an alien artifact recovery mission with protoss opposition. The map used the twilight tileset. Neither the mission nor any mention of Jotun is in the final game.
The jötnar are a group of giants, monsters and minor gods in Norse mythology.