The Celestial Spirit World is the dimension where the Celestial Spirits reside.
The Celestial Spirit World is the place where all Celestial Spirits spend their time when they are not being called up by their summoners. It is presumably ruled by the Celestial Spirit King. Being in the world seems to have some sort of rejuvenating effect on the spirits, restoring their health after being in the human world which, over long periods of time, can potentially kill the spirit. The reverse is also possible: humans are unable to breathe in their world, so after a period of time, albeit a much shorter one, they would die. Such an occurrence (a human entering the Celestial Spirit World) is a serious breach of contract. This rule however, is not absolute, since Natsu survived an extremely brief period in the Celestial Spirit World when he caught hold of Virgo just as she passed through the spirit world to reappear elsewhere in the human world at Everlue's command. This rule was even lifted once when the Celestial Spirit King invited Team Fairy Tail into the Celestial Spirit World for a celebration. One of the places in the Celestial Spirit World is a restaurant where patrons can see auroras, which was mentioned by Scorpio. A human can stay in the Celestial Spirit World for a short time if he or she wears Celestial Spirit clothes.
The time in the Celestial Spirit World is different with respect to the human world: a day in the Celestial Spirit World is approximately three months in the human world.
It seems to have several different planet-like orbs floating in the air and at first glance, the void appears to stretch on infinitely.