Indicated Airspeed (IAS) is the speed shown on the aircraft’s airspeed indicator. It is based on pitot-static pressure and represents how much aerodynamic force (dynamic pressure) the airflow is producing on the aircraft, not how fast you are moving across the ground. IAS is the primary speed reference for takeoff, landing, stall margin, and maneuvering because it relates directly to lift and control feel.
In DCS World, IAS is the speed you will typically fly by for patterns, approach speeds, formation work, and many performance limits. It can differ significantly from True Airspeed (TAS) at higher altitude, where the air is thinner: IAS will read lower even if the aircraft is actually moving faster through the air. Most HUDs and cockpit tapes default to IAS (often labeled KIAS).