z axis: The third axis in a three-dimensional chart. It is used to represent depth.
zero-based index: An index in which the first item has an index of "0" (zero).
zoom level: The degree to which a portion of an image, document, or other screen object is made to appear closer or farther away relative to its default appearance. This value is usually expressed as a percentage of the default appearance.
z-order: The rendering order of an object on a z axis.