The terraforming is a process by which the ecosystem (atmosphere, vegetation…) of a planet or exoplanet is transformed to be suitable to human life. This process takes generally several centuries.
The official (and more general) term for terraforming is “ecogenesis”. The ecogenesis can be applied to extraterrestrial process of a planet transformation.
You can notice that terraforming isn’t science fiction anymore because some studies (notably at Nasa) are currently in progress to terraform Mars.
Examples :
- The Mars series, by Kim Stanley Robinson (unmissable)
- Le rêve des forêts (Saga d’Argyre series), by French author Gérard Klein
- Stargate SG-1, episode 4×09 «Scorched Earth »