What is the difference between countersinking and counter boring?

Countersinking is the forming of a shallow conical shape into a hole or fastener position to accommodate the matching conical head of a flat head screw. Generally, counterboring is the forming of a much deeper, squared bottom, cylindrical area at the origin of a hole or fastener position to accommodate and receive the head of a round-headed fastener, such as a socket head cap screw. Both processes are for the purpose of positioning the fastener such that its head is flush with or below the surface of the component which it is fastening. "Recessed" as it were.