Gravity Manipulation
From Halopedia, the Halo wiki
Template:Category The Covenant have the technology to alter gravitational fields and use this technology in varying ways: in their ground vehicles, on their starships (so their crews do not have to operate in a zero-g environment), and in their "gravity lifts". They use these gravity lifts to ferry troops, vehicles, and supplies to and from their ships and planet surfaces. It is not entirely known how the Covenant's gravity technology works, but UNSC scientists have adapted several peices of scavenged debris into current UNSC ship designs.
A recent skirmish with Covenant troops leads to the belief that they may also have a weapon based on this gravitational technology, a sort of "gravity rifle". It is unknown what this weapon's capabilities are, or even if it truly exists.