Definition:Cartesian Coordinate System/X Coordinate

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

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

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

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

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

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

Also known as
An archaic term for the $x$ coordinate which is sometimes seen is abscissa.

Some sources hyphenate: $x$-coordinate.

Also see

 * Definition:Y Coordinate
 * Definition:Z Coordinate