What is formal?
There are four categories of formal:
 
White Tie (or Full Dress)
Classic Black Tie
Morning Wear
Creative Black Tie

Classic Black Tie

Classic Black Tie has more variation than White Tie in the styles that may be worn, however Black and White is the theme that underpins this dress standard. Wear: either black tails, black dinner suit or white dinner jacket & black trousers (tuxedo), white formal shirt, black vest or cummerbund, black formal neckwear and a white pocket hanky.

 
What makes my outfit formal?