Yes, IAS is the indicated airspeed - which the wings are flying at. Obviously this is most important for lift, drag, (stall) and control response.
As italia suggests; airspeed is measured as air molecules causing a pressure rise in the pitot probe due to the forward motion of the aircraft. This pressure is then corrected for many factors such as probe position error, instrument reading error, atmospheric density, etc. etc. to give an IAS reading in the cockpit. I invented a long mnemonic to remember all the CAS, EAS etc. to pass my ATPL exams, but have forgotten it now! The higher you fly, the less dense the air gets, so there are fewer air molecules causing less pressure in the pitot tube for a given speed. Therefore although an observer might see that you were flying at say 280knots, your cockpit gauge might only read 220knots. The former is the TAS, (true airspeed), the latter is the IAS.
Mach is the speed of sound for a given atmospheric density and temperature and is the speed of a pressure wave - which is what sound is - and is around 720Knots, depending on atmospheric density. Aircraft have a Mach indication because at high altitude and speeds, the speed of the pressure wave becomes important for the aerodynamics of the wing and fuselage; If the aircraft is flying at or faster than Mach 1, the pressure 'message' to the air molecules ahead of the aircraft to get out of the way cannot reach them before the aircraft actually does, and this causes a huge increase in drag. Speeds approaching Mach 1 can be seen over the tops of the wings even when the aircraft is flying below Mach 1, so aircraft are designed to have a maximum economic Mach number, in the region of say 0.73 to 0.84, although speeds greater than Mach 1 can be designed for, e.g. Concorde.
Ground speed is only really important for predictions of estimated time of arrival, and how much fuel you will use, which the wings don't care about, although Airbus for one also use groundspeed as a function in approach airspeed calculations.
Last edited by Uplinker; 2nd Apr 2013 at 16:07.