The name Junction technically referred to multiple planets or planetary objects used for Spacing Guild operations.
However, the name usually referred to one specific planet, formerly known as Kolhar, which had almost no natural population, and was was founded by Aurelius Venport, VenKee Enterprises, and Norma Cenva.
This main planet served as the headquarters for the Spacing Guild and its bank. It was also the location of the only Navigator school. The surface of the planet was almost completely covered with landing fields and repair bays for Heighliners.
In the Dune universe novels written by Brian Herbert and Kevin J. Anderson, Junction was also the location of the Navigator's Field, where Guild Navigators who had died were memorialized, and the mysterious Oracle of Infinity, a clearplaz globe with which the Navigators would "commune."