a reference axis of a three-dimensional Cartesian coordinate system along which the z-coordinate is measured
z-axis in American English
(ˈziˌæksɪs)
nounWord forms: pluralˈz-ˌaxes (ˈziˌæksiz)
Geometry
in a three-dimensional Cartesian coordinate system, the axis that is perpendicular to the x-axis and the y-axis and that is used to measure or plot the values of z