Rate of variation between two points of a line or a segment in a Cartesian plane.

The term

*slope*of a line is synonymous with the**highest degree coefficient**of the line. The slope indicates how the line*rises*when we read it from left to right.- In a Cartesian plane, the slope
*m*of the line that passes through two given points P(*x*\(_{1}\),*y*\(_{1}\)) and

Q(*x*\(_{2}\),*y*\(_{2}\)) is the ratio of the variation of the y-coordinates to the variation of the*x*-coordinates. - When the Cartesian reference point is
**orthonormal**(perpendicular and normed axes), this ratio is called the “slope” and the Cartesian graph is a Cartesian plane. In that case, the slope is the tangent of the angle that the line forms with the*x*-axis. - When the Cartesian reference point is
**not orthonormal**, we must use the expression “rate of variation” instead to refer to this ratio.