In Interstellar, what is the name of the planet where time passes very slowly?

In Interstellar, the planet where time passes very slowly is Miller's planet. It orbits the supermassive black hole Gargantua, whose immense gravity creates extreme time dilation near the planet's surface.

The film establishes that roughly one hour on Miller's planet equals seven years for observers farther away from the black hole. This effect follows the real scientific idea predicted by Einstein's theory of general relativity: clocks run more slowly in stronger gravitational fields. The planet also experiences enormous tidal waves because of its proximity to Gargantua.

Miller's planet is named after astronaut Dr. Laura Miller, whose mission was sent there before the events of the film. When Cooper and Amelia Brand land, they discover that Miller likely died shortly before their arrival, but the time spent searching for her causes decades to pass for people waiting elsewhere.

Gargantua is the black hole, not the planet. Mann's planet and Edmunds' planet are other worlds considered as possible homes for humanity, but neither is the location of the film's dramatic extreme time dilation.