Other forms: terraforming; terraformed; terraforms
To terraform is to alter a celestial body to make it livable for humans. Some scientists imagine terraforming Mars to support a colony of earthlings — but don't hold your breath (which you'd have to do on Mars, because it has almost no oxygen).
The concept of terraforming distant planets is common in science fiction, but it's not likely to happen in our lifetime. Creating a breathable atmosphere on Mars could take hundreds or even hundreds of thousands of years! And then there's the issue of altering the planet's magnetic field to keep the atmosphere in place, dealing with the toxic soil on the red planet, getting liquid water to support life, etc. With current technology, it's not possible to terraform Mars — but maybe humans of the future will be marslings, not earthlings.