Black Tie means formal. Men wear tuxedos, women wear cocktail dresses, long dresses or dressy evening separates.
White Tie means ultraformal. Men wear full dress, with white tie, vest, shirt and cummerbund. Women wear long gowns.
Formalusually means the same as Black Tie, but in some trendier cities like New York or Los Angeles, it could mean a black shirt, no tie, with a tux. Women wear cocktail dresses, long dresses or dressy evening separates.
Ultraformal means White Tie. Men wear full dress, with white tie, vest, shirt and cummerbund. Women wear long gowns.
Black-Tie Optional or Black- Tie Invitedmeans you have the option of wearing a tuxedo, but it should clue you in to the formality of the event, meaning a dark suit and tie would be your other option. Women wear cocktail dresses, long dresses or dressy evening separates.
Creative Black Tie leaves room for trendy interpretations of formalwear. He can go more modern with a tux — maybe a black shirt, no tie. She wears long or short dresses or evening separates (maybe a long lace or sequined skirt with a sleek cashmere sweater).
Semiformalis the trickiest of all dress codes. Usually it means that tuxes are not required, nor are long dresses. An evening wedding (after 6 p.m.) would still dictate a dark suit for him and a cocktail dress for her. Daytime semiformal events mean a suit for him and an appropriate short dress or dressy suit for her.
Cocktail Attire means short, elegant dresses for her and dark suits for him.
Dressy Casual or “California business casual” usually means no jeans or shorts. Similar to business casual, but a tad dressier.
Casual generally means anything goes.
Informal can mean the same as casual. However, when associated with a wedding or other special event, some form of decorum and good taste should prevail. A dress for her or a nice pair of slacks and shirt for him are informal, but respectful of the event.