In computer graphics, texture splatting is a method for combining different textures. The method works by applying an alphamap to the higher levels, revealing the layers underneath where the alphamap is partially or completely transparent. The term was coined by Charles Bloom.
Terrains can also be split into chunks where each chunk can have its own textures. Say there is a certain texture on one part of the terrain that doesn’t appear anywhere else on it: it would be a waste of memory and processing time if the alpha map extended over the whole terrain if only 10% of it was actually required. If the terrain is split into chunks then the alpha map can also be split up according to the chunks and so now instead of 90% of that specific map being wasted only 20% may be.