The international standard ISO/IEC 9995-2 calls it Alternate key. For example, simply pressing A will type the letter 'a', but holding down the Alt key while pressing A will cause the computer to perform an Alt+ A function, which varies from program to program. Thus, the Alt key is a modifier key, used in a similar fashion to the Shift key.
The Alt key Alt (pronounced / ˈ ɔː l t/ or / ˈ ʌ l t/) on a computer keyboard is used to change (alternate) the function of other pressed keys.
