The
grade (also called
slope,
incline,
gradient,
pitch or
rise) of a physical feature, landform or constructed line refers to the tangent of the angle of that surface to the
horizontal. It is a special case of the
gradient in calculus where zero indicates
gravitational level. A larger number indicates higher or steeper degree of "tilt". Often slope is calculated as a ratio of "rise" to "run", or as a fraction ("rise over run") in which
run is the horizontal distance and
rise is the vertical distance.