noun. The basic unit of a three-dimensional digital representation of an image or object.

noun. the three-dimensional analogue of a pixel; a volume element representing some numerical quantity, such as the colour, of a point in three-dimensional space, used in the visualisation and analysis of three-dimensional (especially scientific and medical) data

"The smallest brain area called a voxel that fMRI can measure is usually a 3mm to 5mm three-dimensional volume."

pixel  texel  triangle