Formal or Black-Tie Optional

 

As the wording here suggests, this dress code is slightly less formal than a black-tie wedding. So, a tuxedo isn't required, but can still be worn if preferred. If opting for a suit, however, a formal black suit, white shirt, and a conservative tie are acceptable. For women, the outfit choices remain the same: a black floor-length gown, a fancy cocktail dress, or a dressy pantsuit. In fact, there isn't much of a difference between black-tie and black-tie optional, although Mae says it's more acceptable to wear a dress that shows the ankles (which is not true of a black-tie dress code). -brides.com