1. In reflection seismic work as a property of a set of data, the position midway between source point and geophone (the midpoint), under which the point of reflection is located if the reflector is horizontal and if velocity layering is also horizontal, and if wave conversion is not involved. Earlier called the ‘‘reflection point.’’ 2. Sometimes used for reflecting points in the subsurface, in which case its location may be different for every event, depending on the reflector’s dip and depth and the velocity distribution. 3. In refraction work, the point for which the depth to a horizon has been calculated, usually the point where the headwave energy leaves the refractor to travel to the geophone. See Figure D-9. See also conversion point.