When using the <tile> token, multiple textures can be used to cover a model, rather than a single, much larger, texture. It is the notation at which it is exported in UV texture space. This starts at 1001 (0,0) and continues in U for another 10 offsets. It then progresses onto the next row of V, meaning for every 10 in U it moves 1 in V.
You can use a single File texture to open textures composed of multiple images that correspond to the grid tiles in your UV layout. You can, therefore, open and render high-resolution textures produced by 3D painting applications such as Mudbox, and is a better alternative to using UVsets.