Definitions for "Departure angle"
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.