Refers to the area of the graphical memory used to store the Z, or depth information about objects being rendered. The Z-buffer uses the value of a pixel to determine whether to place it in front or behind another pixel. Z-buffers calculations help to prevent any background objects from replacing/overwriting any objects that are in the foreground of the frame buffer.
ZPS stands for ‘Zero parallax setting’. The ZPS means to control the screens parallax in order to place an object in the plane of the screen. Prior terminology says that left and right images are converged when in the plane of the screen.