Is hypersonic Mach 4+ ?

Supersonic and Hypersonic strike weapon info here http://www.atk.com/AdvancedWeaponSystems/advanceweaponsystems_globalstrike.asp

Pic of HyFly

I don’t know that there is an “official” hypersonic speed. It used to be that you’d only see it applied to things about a mile per second and up but now that the term “hypersonic” has become in vogue you see it applied to damn near anything that goes faster than Mach 3 or so.