In "current" language it means: "a very distant place; end of the world". But “cu” could also be (but it is not): the coins that Judas received if they were made of copper (chemical symbol Cu); the buttocks (cu) of Judas; the abbreviation of the English term “see you”; the name of the letter Q in Castilian.
But the “very distant place” exists. It is in the Azores, more precisely on the island of S. Miguel, in Paupique, next to Serra da Tronqueira, close to the village of Vila Franca do Campo.