The Halee system was a star system in the territory of the Klingon Empire. Exile to a planet in this system was an option for renegade Klingons who wished to find honor by fighting to the death.
In 2364, Lieutenant Worf recommended this system to Captain K'Nera as an option to a dishonorable death by execution for Korris and Konmel. K'Nera agreed that under any other condition, this would be preferable. However, due to the conditions at hand – the alliance with the Federation and the threat these two Klingons posed to it – there was no other option for them. (TNG: "Heart of Glory")
In 2371, the location of the Halee system was labeled in the star chart Data and Picard were studying in stellar cartography aboard the USS Enterprise-D. (Star Trek Generations, okudagram)