Terraforming is altering a planet or moon to make it habitable for humans. If you dream of living on Mars one day, you'll be cheering on any scientific advances in terraforming.
Astronomer Carl Sagan is credited with the earliest terraforming concept, a 1961 theory about how scientists might change the atmosphere of Venus so that humans could live there safely. The enormous scientific and economic challenges to terraforming any known planets make this, as of now, a hypothetical idea. The word terraforming was coined in 1942 by science fiction writer Jack Williamson, from the Latin terra, "earth," and form, "shape or mold."