An Instant Air Dash (IAD) is quickly jumping and air dashing from a standing position.
Performing an IAD
Traditionally it is performed by entering .
An air dash is performed by entering while airborne. The counts as both a jump input and a forward input. You then enter to finish the air dash input. Try to input the IAD with the same timing you would enter a normal dash.
Minimum Height
If you have problems performing this, remember that you can not immediately air dash after jumping, you must reach a certain height before you can air dash (varies by game). Try delaying slightly.
Mid-Combo IAD
Dash Macros
Games with button macros for dashes can do the same thing by pressing any upward direction, then pressing the dash macro.