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.
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")
The Halee system appeared in the starchart Data and Picard were studying in Stellar Cartography in 2371. (Star Trek Generations, display graphic)
According to the Star Trek: Star Charts (pg. 63), Halee was a K class star with a magnitude of +5, which was the same brightness as Sol.