Terraforming
From Halopedia, the Halo wiki
Terrforming is the process in which a planet is changed or "formed" to suit the needs of those terraforming the planet. It normally involves inserting plants and/or flora, introducing new minerals or substances, and just plain changing it to fufill the required goals for the planet in question. Onyx is the only planet known to not have needed terrsforming.
