Uncharted Islands are islands in Dragon Quest Monsters: Joker that you sometimes go to instead of going to the island you were trying to go to. There are several types of uncharted islands.

Slime Islands

Slime Islands are inhabited by slimes, she-slimes, and behemoth slimes. They are often searched for, as they are the only way to obtain behemoth slimes which are useful in synthesis.

Dragon Islands

Dragon Islands are inhabited by Frou-fries, Argon Lizards, Frou-frous, and Great Argon Lizards. These are also often searched for as the Great Argon Lizard and the Frou-frou have great skills for synthesis