The speed of an aircraft relative to its surrounding air mass. The unqualified term "airspeed" means one of the following:
  1. Indicated Airspeed- The speed shown on the aircraft airspeed indicator. This is the speed used in pilot/controller communications under the general term "airspeed." (Refer to 14 CFR Part 1.)
  2. True Airspeed- The airspeed of an aircraft relative to undisturbed air. Used primarily in flight planning and en route portion of flight. When used in pilot/controller communications, it is referred to as "true airspeed" and not shortened to "airspeed."

Source: Pilot Contoller Glossary (PCG)