From Halopedia, the Halo wiki
Halo 4: Original Soundtrack Volume 2
Cloud City is the fourteenth track on Volume 2 of the Halo 4: Original Soundtrack. A portion of this track is used in War Games to signify a player's approaching victory.
The track's name refers to an artificial habitat that floats above the gas giant Bespin in Star Wars Episode V: The Empire Strikes Back.