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A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions. On some keyboards/computers, function keys may have default actions, accessible on power-on.

F1 through F12 may have a variety of different uses or no use at all. Depending on the installed operating system and the software program currently open will change how each of these keys operate. A program is capable of not only using each of the function keys, but also combining the function keys with the ALT or CTRL key, for example, Microsoft Windows users can press ALT + F4 to close the program currently active.