Subsonic flow

From CFD-Wiki

A flow in which the Mach number is less than one everywhere is known as subsonic flow. Typically, if the freestream Mach number is less than about 0.8 then the flow is usually subsonic everywhere. However in some situations like flow over a highly cambered airfoil, the Mach number may locally exceed unity due to acceleration of the fluid in the curved regions. Subsonic flows are characterized by the absence of shocks which appear only in supersonic flows.