A voxel is a three-dimensional pixel (a volume pixel) that is, a pixel with a third coordinate after the usual pair.

Voxels are often used in computer graphics to obtain an approximation of 3D displays. A single "layer" of voxels is not a 3D display in the strict sense: if we assume that the coordinates refer to a plane, only one height is possible at any given position, and so multiple objects at the same planar position are not possible.

Despite this, voxels are very useful for map displays and other data format where such a limitation is not important.

Sometimes, true 3D displays use the word voxel to speak about a real 3D pixel. For example, one display could be able to show 512×512×512 voxels arranged in a cube.