Pure Land

The is the afterlife in which the souls of earthly beings generally reside in death. Souls that have been sealed, such as by the Dead Demon Consuming Seal, cannot enter the Pure Land until the seal has been released. Furthermore, only those souls that reside in the Pure Land can be reincarnated with the Summoning: Impure World Reincarnation.

Purgatory
To arrive at this place, the deceased has to go through a middle plane of existence, where other people such as relatives or friends can be met. People residing in this plane are those who haven't been able to move on because of earthly regrets or because they decided to wait for someone. Obito noted that chakra is the power that connects this plane and the real world, and as such he was able to teleport back to the world of the living to meet Kakashi Hatake once more.

Trivia

 * Hagoromo Ōtsutsuki was able to momentarily call forth the spirits of the previously deceased Kage from the Pure Land, a feat referred to as godly by Kakashi, to help with the summoning of Team 7 and the tailed beasts from Kaguya's dimension.