The Tarn Neutral Zone, also called the No Entry Zone, was an area of space between the borders of the United Federation of Planets and the Tarn Empire. It was established in 2165 at the end of the Federation-Tarn War.
The Tarn knew they couldn't beat the Federation in a stand up fight and the Federation wasn't interested in a dragged out conflict. Both sides agreed to cordon off a couple of hundred thousand cubic parsecs as a buffer zone. The region was known to be devoid of sentient life before the zone was established. The neutral zone effectively closed the discussion as to who was at fault and no permanent treaty was ever established between the two governments. In 2367 the No-Entry Zone was open to ships on both sides. Starfleet decided that the USS Enterprise (NCC-1701-D) was needed for a show of force and to scan this area. The Enterprise was the first Federation starship in the zone in over 200 years.
While in the Tarn Neutral Zone, the Enterprise-D discovered the wreckage of the Tarn Imperial Fleet vessel Rashasa and the Starfleet vessel USS Verdun in the Torgu-Va system. The survivors from the two vessels had landed on Torgu-Va and were continuing to fight the war that had ended some 200 years earlier.