Definition:Slope/Straight Line

Definition
Let $\LL$ be a straight line embedded in a Cartesian plane.

The slope of $\LL$ is defined as the tangent of the angle that $\LL$ makes with the $x$-axis.

Also defined as
Some sources define the slope of $\LL$ as the actual angle that $\LL$ makes with the $x$-axis, rather than its tangent.

On we specifically mean the tangent of that angle.