See yaw.
The vertical or up & down movement of the engraving spindle.
See x-axis.
An imaginary line at right angles to the X and Y axes. Usually the same as the vertical axis. This IS the all important third axis in a 3-dimensional coordinate system.
[n] - the third axis in a 3-dimensional coordinate system
Represents the depth of an object when working with 3D coordinates.
 movement towards and away from the camera is in z
Axis perpendicular to both X and Y axes. 
noun the third axis in a 3-dimensional coordinate system
The plain of movement a road vehicle cant access. 
(in a three-dimensional Cartesian coordinate system) the axis along which values of z are measured and at which both x and y equal zero.