Control key

A Control key (CTRL) is a modifier key found on most modern keyboards. Though Mac keyboards usually include this key, the equivalent modifier in macOS is the Command key (⌘).

Usage
Holding down a control key while pressing and releasing letter keys or certain other keys generates a "control character". For example, holding control and hitting "A" generates control-A (ASCII code 1). The ASCII code for the control character is generally 64 less than the value for the unmodified character.

Standard PC keyboards typically have two control keys, both labeled "Ctrl", at the bottom left and bottom right of the main block of keys. The control key does not generate any character on its own but most modern keyboards and operating systems allow a program to tell whether each of the individual keys on the keyboard (including modifier keys) is being pressed at any time.