What is "white-tie"

White-tie \White-tie\, a. requiring formal evening clothes, usually interpreted as a white bow tie and a tailcoat for men, and a formal evening dress for women; -- as, a white-tie reception at the embassy. Contrasting with black-tie and informal.

a. Very formal; usually requiring a tailcoat for men.

adj. requiring white ties and tailcoats for men; "a white-tie occasion"