In computing, a modifier key is a special key on a computer keyboard that modifies the normal action of another key when the two are pressed in combination.
For example, + in Microsoft Windows will automatically close the program in an active window. In contrast, pressing just will probably do nothing unless assigned a specific function in a particular program. By themselves, modifier keys usually do nothing.
The most common modifier keys are:
-- "control"
-- "alternative"
-- "alternative graphic", used to obtain special symbols from the keyboard. If a key has a third symbol on it (sometimes in a different colour or on the vertical edge of the key), then will elicit that symbol. Under Microsoft Windows, is equivalent to .
, of course, is the oldest in terms of keyboards in general as it originates from typewriters and is usually used to make uppercase letters when typing.
Apple Macintosh computers also have the special key with the Apple Computer logo and a proprietary symbol that looks like a four-leaf clover (Unicode code point U+2318, or ⌘). is also replaced with the