Itachi Uchiha's soul returning to the Pure World.
The Pure World (浄土, Jōdo) is the afterlife in which the souls of earthly beings generally reside in death.
Trivia
- Souls brought back to life using the Summoning: Impure World Reincarnation seem to have no memory of the afterlife. Rather, their memory stops at the moment of death as if it is trapped, frozen, within the body.