The Treaty of Axanar, also called the Axanar Peace Treaty, was a diplomatic agreement made to conclude the Four Years War between the United Federation of Planets and the Klingon Empire in reference stardate 1/9806.13 (c. 2250s), following the Axanar Peace Mission. (FASA RPG modules: The Federation, Star Fleet Intelligence Manual: Agent's Orientation Sourcebook)
The Treaty called for all Klingons to withdraw "to the opposite side of Orion space", which was a largely undefined area at the time. The Rigel Demilitarized Zone Commission defined it with the creation of the Orion Neutrality Area. (FASA RPG module: The Orions: Book of Common Knowledge)