Definition - What does Toggle Key mean?
A toggle key is a key that is used to turn a function on or off, or to switch between two functions. Examples of toggle keys are the caps lock key, number lock key and scroll lock key. A toggle key can also be used as an accessibility option to alternate the input mode of keys.
Techopedia explains Toggle Key
A toggle key toggles the input from other keys on the keyboard between different input modes. The most commonly used toggle key is the caps lock key, which alternates the letter keys between uppercase and lowercase. Num lock is another toggle key which helps to input numerals from the numeric keyboard and is turned on by default. Another example of a toggle key is the scroll lock key, which allows arrow keys to scroll through window's contents and allows users to scroll without depending on the scroll bar. The insert key is another example of a toggle key, and it toggles between overtype mode and insert mode while entering text.
A toggle key, unlike modifier keys, is turned on or off when pressed —they need not be held down while pressing other keys. Most keyboards have lights indicating whether the keys are switched on or off. Some operating systems and applications also display the toggle key status on the screen.