At the request of new members I have decided to fix the bug in my voxel raster example. This was the first thing I wrote when I joined ENIGMA.
There are two types of voxels, one is like Minecraft involving cubes, the other involves raster graphics. Basically you just ray-trace every pixel of the display into the scene. This made it possible for early 90's games such as Outcast to do special effects such as bump mapping and water reflections.
Size: 3.19 MB
This technique was also used in the first Comanche games for rendering the terrain.
Most of Wikipedia's information covers Minecrafts version of voxels.http://en.wikipedia.org/wiki/Voxel
Which I am going to touch up as well with some elaborated information. My method is similar to 3D scanning and what satellites do.