The term "Trans-Briar Patch" encompasses the region approximately 120 lightyears square on the opposite side of the Briar Patch nebula from Earth. Starfleet activity is centered in the New Canada system on the edge of the Briar Patch, and newly-opened Federation territory extends more than 120 lightyears coreward into the former Mulluran Empire. (Star Trek: Banshee Squadron)
The Trans-Briar Patch sectors are home to the Son'a and their allies, the Elora and the Tarlac. The remnants of the Mulluran Empire are also here, wedged between the Ferengi Alliance and the Breen Confederacy. Other systems formerly under the control of the Mullurans include Polon, Rostella, and G'Kra.