Definition - What does Impact Pressure mean?
Impact Pressure is the difference between the static pressure and the total pressure. It provides the calibrated airspeed reading while input to airspeed indicator. Air data computers with the static pressures and inputs of the pitot can provide the Mach number and true airspeed if the static temperature is known. British authors match the definition of dynamic pressure to that of Impact Pressure as they define dynamic pressure as difference between the static pressure and stagnation pressure.
Petropedia explains Impact Pressure
Impact Pressure and static pressure cannot be considered similar although there is a close agreement between both as far as measurement of airspeed is concerned till the Mach is measured as 0.3. These pressures are not similar regardless of flow being supersonic or subsonic. An additional problem of entropy can be noticed for supersonic flow across a strong wave of bow shock in front of pitot probe that decreases the total pressure. Compressible dynamic pressure or dynamic pressure are the terms which are used by the authors in the compressible flow fields rather than Impact Pressure.