Infinite Worlds is the second World Type, added in 0.9.0. It enables you to explore your world almost infinitely. It looks like "Default" World Type from PC.
Sadly, Apple products of the 4th generation and lower will not be able to experience this feature because 4g iPods and ect. have a single core processor, while 5g Apple products have double core processors, which can handle the infinite terrain. Note: 4g Apple devices can join any 5g devices in Multiplayer and experience the infinite worlds. It is also an option to expand your world without the infinite terrain. However single core processor doesn't just apply to Apple, any devices in general with single core processor won't have infinite worlds.
For Android, the infinite worlds are available on all devices, but if you have single core device, you must turn off option "Limit worlds" in Experimental, but you will cause lags.
Sadly, a disadvantage of infinite worlds is the fact that it is much easier to get lost now, as there are no more boundaries that one gets stopped at, and therefore the player can wander around aimlessly, possible getting further and further away from their home.
How to get it before 0.9.0
The server "infinity.lbsg.net" has infinite terrain without the 0.9.0 update. Click here to see the rest of the Liifeboat servers.
Note: These are the direct IPs, not the server names.