It doesn't exist naturally on earth, the sun creates it but it bounces off the atmosphere. So it's just collecting on the surface of the moon, it's something ridiculous like enough possible fuel in just the sea of tranquility to power the US at current rates for hundreds of years.

When I first read about it, the story was that it was discovered as a by-product of servicing nuclear weapons and the physicists were like "man, wish we had more of this" and then like 20 years later the nuclear physicists and the astrophysicists were chatting, the nuclear bros brought it up and the space bros were like "that shit is literally just all over the moon". Not sure if true but funny story.