measurement of the angle of the bottom plane of a shoe heel against the ground plane, or sometimes of the height up from the ground plane to the rearmost point of a heel that meets the ground at an angle
Many shoes, and especially many low-heeled men’s shoes, are designed with no heel spring at all, so the bottom of the heel lies flat against the ground. Other shoes are intentionally designed to leave a slight gap between the back of the heel and the ground when set on the bench, to be flattened out by the weight of the wearer when worn.