The world border is a border that is dynamically created inside the audio environment of the editor and your game for each world. The distance of the border depends on the four outer building blocks of your game. The border will be made at a number of grid blocks distance from the building blocks that are at the outer positions of the audio environment.
You can change the distance at which the border will be created form these outer building blocks if you select border distance. You can give an integer value that represents the number of gridblocks which are also virtual meters.
You can also change the sound that the world border makes when the player reaches it.