From Halopedia, the Halo wiki
The thruster pack is a propulsion unit used by Sangheili Rangers to maneuver in zero- to low-gravity environments. Unlike the antigravity pack, the thruster pack appears to use chemical-based thrusters for propulsion similar to the human's Series 8 jetpack.
Concept art for the Covenant thruster pack.
A thruster pack in Halo: Reach.
Thruster pack patterns in Halo Reach.