The Maw is a piece included in the Halo: Original Soundtrack. It is also used as part of Dust and Echoes.
It starts playing at the beginning of the level The Maw, the namesake for the song, when John-117 and Cortana, riding in a Banshee head back to the UNSC Pillar of Autumn.
This piece forms the base for the Halo 2: Original Soundtrack piece, Remembrance, and the intro of Ghosts of Reach.
It was remade in the Halo: Combat Evolved Anniversary Original Soundtrack as Yawning Chasm.