Reason:
voxels have come up in enough discussion where i decided it would be better if i just wrote about it.

Introduction:
a voxel is a "cell enumeration method".
To visualize what a voxel really is, just think of 3d graph paper. The voxels are the actual grid boxes.

the smaller the grid spacing the smaller the voxels get. in voxel methods, each "grid box" or "voxel"  is important to the application and render, where as in polygon representation in most cases it is just the actual position of the vertices.


Often the voxel based application requires more detailed analysis on the visualization data.
voxel usage is primiarly found in the medical feild, particle simulations, detailed fluid simultions (viscosity flow), nuclear simulations and things of this sort.



why do those people use voxels?
In most cases the application needs to alter the "voxel" in a very controlled environment. by only having "grid boxes" it' becomes much easier to control and manipulate the data.
 

if you still not have gotten a mental image of what a voxel is just consider that a rubex cube and a "voxel world" are rather similar. just consider the cube to the the world, and each mini cube to be a voxel.

Although this was a rather brief summary of a "voxel" i have tried my best to keep it short and to the point. If you are still intersted on this topic, 
the reader is directed to "computer graphics principles and practice" 
Second edition. Authors : Foley, ....
see my book list, it's up there.
 

akbar A.