From Halopedia, the Halo wiki
Flollo is the fifth track in the Halo Wars: Original Soundtrack.
The track is an ambient track with basses playing its main melody, accompanied by synthesizer patches like leads and pads. The play in ambiance, with short snippets of soft percussion near the end.
The soundtrack's bonus DVD includes a 5.1 channel surround mix.
The track plays randomly as a backing track during gameplay on any campaign or Skirmish levels in Halo Wars set on the surface of the Etran Harborage (though with exception of two campaign levels), including: