z (axis) + variant; from the three dimensions visualized for the character space. The x-axis separates characters by semantics (function and meaning, e.g. A from B), the y-axis separates them by their general form (abstract shape, e.g. A from a), and the z-axis by their actual shape (minor details such as typeface, e.g. a from a).
z-variant (plural z-variants)