Seek for clarification on voxel in 3D texture

Hi all,

I would like to ask for clarification on voxel in 3D texture.
FYI, i have heard a lot about voxel and do some research about them but i cant seems to actually get to know what they really are??
Can i have some clarification about voxel in 3D texture and how to actually access them.

Thanks alot:o:o