Farlands is only in Pocket Edition, it’s about 12550821 blocks from any world spawn and it’s where terrain is generated awkwardly. It’s a wee tough to explain to hopefully you’ll understand. Here’s some pictures to show you. Enjoy!
(This can happen in any world but if you don’t have the desire to walk that many blocks from spawn to see this, you can download a map that spawns you in it. Download is below)