Air Traffic Controlers speak via radio to the pilots so as to give them clearance to taxi, take off, land and to indicate them the route they must follow.
While on radio, pilots identify their aircraft by its registry name, and use words to describe the letters that form it, that way, aircrafts can´t be mistaken by another one.
I: India/Italy (Pakistan).
L: Lima/London (Malaysia, Brunei, Indonesia, Singapore)…
W: Whiskey/Washington (Saudi Arabia).
Most of you might already know this, but I thought posting it so the new members can have at least a superficial familiarization with the ATC.