The usual explanation is 2D : pixels :: 3D : voxels but you might find this more intuitive: typical 3D : vector graphics :: voxels : bitmaps In other words

The usual explanation is 2D : pixels :: 3D : voxels but you might find this more intuitive: typical 3D : vector graphics :: voxels : bitmaps In other words, typical 3D is made of polygons whose vertices are specified to arbitrary precision, whereas voxel-based 3D content is a big three-dimensional array of discrete values. The voxel data can be coarse (like Minecraft) or quite smooth (like an MRI scan), but the distinguishing feature is that the data is discrete.