Box system was a common name for a star system whose outer limits were surrounded by intense electromagnetic fluxes. These fluxes would then interact with the solar wind, hindering hyperspace travel. One such system was the Unknown Regions' Rapacc system, which included the planet called Rapacc.
A defining characteristic of box systems was the presence of unusually strong electromagnetic fluxes encircling the outer edges of the system. The interaction of these fluxes with solar wind emitted from the system's star made hyperspace travel difficult and negatively impacted the abilities of navigators, such as Chiss sky-walkers. To access the inner regions of a box system, a starship had to enter via space-normal.
Planets, including gas giants, could create openings in the solar wind, providing easier routes into and out of the system. While these openings were hard to detect from outside without detailed planetary information, they were easier to exploit from within. The characteristics of box systems made them suitable for defensive purposes and for restricting external starship traffic, rendering them ideal for maintenance facilities, supply depots, or concealed staging locations.
An example of a box system was the Rapacc system, located within the Unknown Regions and the homeworld of the Paccosh on Rapacc. After the planet was subjected to a blockade by the Nikardun Destiny, two Paccosh refugee ships succeeded in escaping the system with assistance from Void Guide navigators. Senior Captain Thrawn of the Chiss Ascendancy believed that they had taken advantage of shadows within the system's solar wind to make their escape. Thrawn himself utilized these same shadows during his investigation of the Nikardun alongside Admiral Ar'alani.
The 2020 novel Thrawn Ascendancy: Chaos Rising, authored by Timothy Zahn, featured a box system.