Formal or Black-Tie Optional
 

The wording here indicates something slightly less formal than black-tie is acceptable. So, a tuxedo isn't required, but the event is still formal enough for one to be appropriate. The choices are the same as with black-tie: a floor-length gown, a fancy cocktail dress, or a dressy pantsuit. As far as women are concerned, there's not much of a difference between black-tie attire and black-tie optional attire, 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). Men have the option of wearing a tuxedo, or they can wear a formal dark suit, white shirt, and conservative tie.