The Fabrini homeworld was an inhabited world in the Fabrina solar system, and the homeworld for the Fabrini.

Approximately 10,000 years before 2268, when the ancestors of the Fabrini living on the asteroid spaceship Yonada discovered their world was dying with its sun, they moved underground to protect themselves from the sun. Eventually, they built the Yonada, chose their best people to crew it, and sent the ship on course to another planet before the sun went nova. (TOS: "For the World is Hollow and I Have Touched the Sky")

This planet was only mentioned in dialogue.