gradient

Steepness of a slope (incline or decline), commonly measured in one of the three ways: (1) The angle (called the 'slope angle') the line, path, or surface makes with the ground or horizontal (called 'grade line') expressed in degrees or grads. For example, a 5 degree gradient. (2) Ratio of the vertical distance to the actual distance along the slope (that is, sine of the slope angle). For example, a gradient of 1 in 4 means a vertical distance of 1 unit for 4 units along the slope, expressed as 1/4 grade or 25 percent grade. (3) Ratio of the vertical distance (elevation) to the horizontal distance (that is, tangent of the slope angle).