Nibiru is not real. It is a location in Babylonian mythology. In modern times, it is more commonly associated with a New Age apocalypse scenario called the Nibiru cataclysm.
The idea of the Nibiru cataclysm, where a planet from the outer solar system collides with Earth, dates to 1995. Its primary creator, Nancy Lieder, refuses to give a specific date for the Nibiru cataclysm; this follows the failure of her earlier Nibiru predictions.
Nibiru's existence is rejected by modern astronomers. While numerous dwarf planets and asteroids exist past the orbit of Pluto, none is on a trajectory to collide with Earth and cause the Nibiru cataclysm.