The words voxel and chunk are often used when dealing with Ultimate Terrains, but I’m not sure to understand what it means.
A voxel is an entity that contains some information at a given position in the 3D scene.
In a world made of cubes like in Minecraft, each cube could be considered as a voxel with a value of -1 (cube) or 1 (no cube). With a smooth terrain, a voxel is almost the same but has a float value. A negative value means it is “inside” and a positive value means it is “outside”. It’s a bit hard to understand at the beginning, but you will get used to it after a few days using Ultimate Terrains.
You can see the value of a voxel as the distance between the voxel and the surface of the terrain.
In Ultimate Terrains, the terrain is separated into small parts named chunks. This allows to refresh only parts which need to be refreshed when editing the terrain in real time, instead of computing all the terrain again and again.