direction of flow.; Bow: Occurs upstream of the front (bow) of a blunt object when the upstream flow velocity exceeds Mach 1.

Some other terms:
* Shock front: The boundary over which the physical conditions undergo an abrupt change because of a shock wave.
* Contact front: In a shock wave caused by a driver gas (for example the "impact" of a high explosive on the surrounding air), the boundary between the driver (explosive products)