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.
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.
Performing an IAD mid-combo might require different timing due to hitstop keeping you grounded longer. You can get around this by timing your jump input near the end of hitstop, or not do an IAD and instead input manually after jumping.
IADs can be performed for both forward air dashes and backwards air dashes, the concept is exactly the same, just reverse left/right inputs.
Games with button macros for dashes can do the same thing by pressing any upward direction, then pressing the dash macro.