The Zerg Quarantine Zone is a region of space of the Koprulu Sector, presumably designed to keep the zerg at bay from the rest of the sector. Appropriately, Char is located within this area.
References
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Elder, Josh and Ramanda Kamarga. "Why We Fight." In StarCraft: Frontline: Volume 1, pp. 6–47. Tokyopop, August 1, 2008. ISBN 1427-80721-3.
