Formal, Black-Tie Optional attire is a dress code that allows for a bit of flexibility. Here’s what it generally means:

• Black Tie Optional: This suggests that while a black tie (tuxedo) is not required, it is still a suitable and acceptable choice. Guests can opt for a tuxedo, but it’s not mandatory.
• Alternative to Black Tie: If you choose not to wear a tuxedo, you should wear a dark suit and tie. A dark suit (like navy or charcoal) with a dress shirt and a conservative tie is appropriate.
• For Women: Evening gowns, cocktail dresses, or a sophisticated dressy suit are suitable. Opt for something elegant but you don’t have to go all out with a full-length gown unless you prefer.

Overall, the key is to dress in a way that’s formal and elegant, but with the option to choose a less formal but still very polished look if you prefer.