The home of the felinoid Caitians, named in background material written for the animated series and seen on screen only as a label on a Federation star chart.
Cait is the homeworld of the Caitians, the cat-like Federation species represented by Lieutenant M'Ress, communications officer of the Enterprise in the animated series. The name comes from background material prepared for that series in the 1970s and was taken up by reference books, novels and games.
On screen the name has had only a fleeting appearance. A chart displayed in the Strange New Worlds episode Children of the Comet marks Cait as a Federation-aligned system in 2259. No episode or film has been set there.
Caitians themselves appear among the Federation Council in Star Trek IV: The Voyage Home, and Lower Decks features the short-tempered Caitian doctor T'Ana aboard the USS Cerritos.