1The process of becoming grey, faded, or paler in colour. Also figurative: the process of losing distinctiveness, individuality, or vitality. Compare to grey out.
2The process or fact of experiencing greyout.
The process or action of causing a menu item, icon, or other element of a user interface to be displayed in grey, or more faintly, especially so as to indicate the unavailability of the option represented.
Early 20th century; earliest use found in Boston Medical and Surgical Journal. From grey + -ing + out, after blacking out.