Slope, also known as "angular coefficient", indicates the degree of inclination of a straight line relative to the horizontal axis. The tangent of the angle between a straight line and the positive semi-axis of the horizontal axis of a plane rectangular coordinate system is the slope of the straight line relative to the coordinate system. If the straight line is perpendicular to the x-axis, the tangent of the right angle is infinite, so the straight line has no slope. When the slope of the straight line L exists, for the linear function y=kx+b, (slope-intercept form) k is the slope of the graph of the function.