scifi
Dave Reid is perfectly correct, "Air speed" without an adjective is meaningless.
Technically, a pitot static system measures a quantity known as Equivalent Airspeed which is the airspeed which would be registered at sea level by the number of molecules which pass by per second at the flight altitude and speed. EAS is the quantity you need to calculate the forces on the airframe, or to know how close you are to flight envelope limits. In short, it is the number you need to know to FLY the aeroplane. IAS,CAS are simply corrections to EAS to account for variations arising from the positioning of the pitots and static ports along with compressibility effects.
True airspeed, on the other hand, will differ from EAS by considerable amounts which depend on the altitude and ambient temeperature. It is the number you need to know to NAVIGATE the aeroplane.
I must say I am surprised to find this sort of discussion in a professional pilot's forum!