AID-Key (IBM 3270 and 5250 Only)

AID Key stands for Action IDentifier Key. An AID key is any key that sends data to the host. Typical AID Keys are ENTER and the PF keys.

AID Keys are necessary because IBM 3270 and 5250 are screen based protocols, as opposed to character based.  The AID key is necessary in order to trigger when screens get sent to the host.