When it come to choosing wedding day attire, the men of the bridal party and the wedding have a much easier time of it than the women. The appropriate clothes are simply determined by tradition, according to the formality and time of day of the celebration. Letting people know what they are expected to wear is essential on your invitations for your wedding. Be as clear as possible in what you mean. A definition may be required. 

BLACK TIE or DINNER JACKET:
Formal evening wear is seen only after six o'clock. To be traditionally correct, men wear a whit pintucked  or wing collar shirt with a black bow tie. With this you must wear long fine black socks, black shoes, black trousers and a black dinner jacket. For formal daytime weddings, choose a classic cutaway coat with grey pinstripe trousers, grey vest and tie.

LOUNGE SUIT or SEMI-FORMAL:
For a man this means matching dark jacket and trousers with a business shirt and tie. For women, cocktail dresses  or the equivelant. The classic tuxedo is proper for a semi-formal evening ceremony.

INFORMAL:
It does not mean what it says. It just means not black tie and not neccessarily a lounge suit. A man may wear a shirt with dress trousers. Woman could wear a similar dress  that you would wear to lunch, a  classic skirt and top or dress.

SMART CASUAL or ELEGANT CASUAL:
Well cut trousers , an open neck shirt would be fine as would a day dress or skirt.

COME AS YOU ARE:
Don't take it literally. What it means is don't put on your finery, but do come scrubbed up and neatly turned out.