Cait is the home planet to the Caitian species. It is a Class M planet and a member of the United Federation of Planets.
Nothing else is known about Cait outside of conjectural fan fiction; the only confirmed member of the species in Star Trek is Lieutenant M'Ress from the Animated Series, and she only appeared in a few episodes.
In general, it is considered likely that Cait is a lush world, and that the Caitians have taken good care of their home planet's ecology. As a hunter species, the Caitians would have hunted countless species to extinction without some controls in place; it is thus likely these controls were developed early in their civilization, and that Caitians have a good understanding of their place in the world's environment.