In side view, the angle between the ground and a line, aft of the vehicle, joining the periphery of the rear wheel and (typically) the rear chassis member or other low component. It represents the size or steepness of a slope or obstacle that can be approached or climbed in reverse without striking bodywork.

the angle between your rear tires and the first rear protrusion that would scrape the ground as you descend off of a hill

Same as Angle Of Approach/Departure.

the angle at which a line drawn from a vehicle's rearmost bodywork and touching a rear tyre meets the ground. It gives an indication of the maximum steepness of a step-down that a vehicle can negotiate without dragging the rear bodywork. Long body overhangs reduce the departure angle. The closer the angle is to 90 degrees the better for offroad work. See also approach angle.

a vehicle's rear clearance angle. This angle is formed by the base of the rear vehicle tire, the rear ground clearance height and the roadway.