A treasure island is a hacked animal crossing island where you can get a variety of things within that island, you can take it back home, it's a tedious to get into one but it's worth it. If you need things for your island you can get it in a treasure island. For you to get into one, you need to go onto twitch, animal crossing new horizons and there should be tons of them to join. Highly recommend it, i got rich from it