The Azure Nebula is a type 11 nebula, the home of the Iccobar and location of the Holocovia system, found on the border between the Federation and the Klingon Empire. The USS Excelsior entered the nebula in 2293 during Captain Hikaru Sulu's ill-fated rescue of James T. Kirk. There he encountered a Klingon battle cruiser commanded by Captain Kang, who attempted to escort Sulu out of the nebula, but was disabled when the Excelsior ignited the nebula's sirillium gas.
During 2384 and 2385, a Borg cube hid in the nebula to avoid detection by Starfleet after the Borg elimination incident. During this time, a Rakelli freighter was assimilated by the cube.
In November 2385, the defeated Borg armada from the Battle of Gateway hid in the nebula, but were found by Alliance forces and escaped through a transwarp aperture to Unimatrix One.
It was at this time an away team from the USS Sovereign stumbled upon the Holocovia system, and explored its fourth planet.