I learned about the meaning of the words pixel and voxel in Andrew Witt's latest book, Formulations.
By the mid-1970s, at the time of March's encodings, the humble cube gained its own computational term of art: the voxel, a portmanteau of “volume” and “element,” the three-dimensional analogue of the pixel. “Element” evokes an atomic, almost chemical simplicity but also the possibility of molecular recombination. As the three-dimensional version of the two-dimensional pixel (“picture element”), the voxel became an atom of digital design and a quantum of total spatial inventories. —Andrew Witt, Formulations