From LQWiki

A dead key is a key on the keyboard that modifies the next key that will be pressed. An example is ` that, when pressed, does not produce any character but waits for the next key press. If the next keypress is an "e", the resulting character is è.

See also

• configuring Keyboards
• http://en.wikipedia.org/wiki/Modifier_key
• http://en.wikipedia.org/wiki/Dead_key
• http://en.wikipedia.org/wiki/Compose_key