Num Lock key
A key that switches the numeric keypad from numeric mode to cursor control mode, and vice versa. In numeric mode, the keys represent numbers even when they are combined with the Shift key, Function key, or Control key. Otherwise these combinations may have different meanings.
The Num Lock key is a toggle key, meaning that it changes the current mode. If the numeric keypad is already locked in numeric mode, pressing the Num Lock key releases it.