In the X Window System, every individual, physical key is associated a number in the range 8–255, called its "keycode". A keycode only identifies a key, not a particular character or term (e.g., "Page Up") among the ones that may be printed on the key. Each one of these characters or terms is instead identified by a "keysym". While a keycode only depends on the actual key that is pressed, a keysym may depend, for example, on whether the Shift key or another modifier was also pressed.