Chaos (planet)

Planet Chaos was the planet where the rain never stopped. This fact showed The Doctor that there was another force was present when he met Amy for the first time, as this force, which was actually the Grace, had stopped time, making it seem that the rain had ceased. (BFA: The Key 2 Time - The Judgement of Isskar)

Planet Chaos was the place where the Chaos Pool, the forge for the Key to Time, was hidden.

It was located in a hyperspatial fold, making the extreme ends of the universe co-adjacent to each other, making the Atrions and the Teuthoidians fight each other in their respective searches for the Pool. This fold was ironed out when the segments in Zara's satchel came into contact with the warp manifold and other equipment within Professor Lydel's laboratory, even though the Doctor warned him not to put the bag near it.

It was also home to the final resting place of the Teuthoidians in one of the many cavernes on its surface. (BFA: The Key 2 Time - The Chaos Pool)