The Neutral Zone: Played straight, although given the nature of the stargate plexus as, essentially, a mesh network, it’s not so much a zone, but a list of Neutral Nexi.  No-one tries to enforce deep space as a neutral zone, mostly because it’s just too damn big and remote to patrol – unless someone leaks the existence of a hidden base out there, anyway.

It’s not even all that common as an entire constellation – usually, the list of Neutral Nexi is a thin surface one system thick, or even a single chokepoint system – because it’s rare for any powers to bother developing the wormhole infrastructure to connect them so intimately to their enemies.  Although there is the Seam as a whole, and particularly the Csell Buffer, which was a semi-developed constellation going by the name of the Csell Reach in between the Galith Waste and Voniensan space shortly before the Silicate Tree turned up and claimed the Galith Waste, and then Things Did Not Go So Well.