You may notice this symbol on your keyboard. This is referred to as 'Function Lock' which locks or unlocks the F row on your keyboard. Your F row may range from F1-F12 or even up to F16. There are small symbols underneath that you can "lock" into place so that they are active instead of the F key feature. To lock or unlock this feature, you can use the key combination of Fn + Esc at the same time, then let go. The same key combination can be used to revert back to using the F keys.