Definition:Cartesian Coordinate System/Z Coordinate

Definition
Consider a Cartesian coordinate system $C$ with a $z$-axis.

Let a point $Q$ be positioned in $C$.

Let $z$ be the length of the line segment from the origin $O$ to the foot of the perpendicular from $Q$ to the $z$-axis.

Then $z$ is known as the $z$ coordinate.

If $Q$ is in the positive direction along the real number line that is the $z$-axis, then $z$ is positive.

If $Q$ is in the negative direction along the real number line that is the $z$-axis, then $z$ is negative.

Also known as
Some sources hyphenate: $z$-coordinate.

Also see

 * Definition:X Coordinate
 * Definition:Y Coordinate