I just googled the term voxel because I’ve been too lazy to prior to this:
noun: voxel; plural noun: voxels
(in computer-based modeling or graphic simulation) each of an array of elements of volume that constitute a notional three-dimensional space, esp. each of an array of discrete elements into which a representation of a three-dimensional object is divided.
I don’t think the Mario game has anything to do with voxels. The EQN one claims to have the terrain set up as voxels, which I suppose we can take for at their word. The term itself is pretty loosely used to describe any modifiable 3D array/matrix.