Page "Cartesian coordinate system" Paragraph 80

The name derives from the right-hand rule.

If the index finger of the right hand is pointed forward, the middle finger bent inward at a right angle to it, and the thumb placed at a right angle to both, the three fingers indicate the relative directions of the x -, y -, and z-axes in a right-handed system.

The thumb indicates the x-axis, the index finger the y-axis and the middle finger the z-axis.

Conversely, if the same is done with the left hand, a left-handed system results.