The dresscode Black Tie is often set for (formal) festive events like; fundraisers and gala’s.
Men wear a smoking; simple like that. A smoking is a black or dark colored tw-piece suit with a shiny lapel. This is to be worn with a crinkled shirt, same-color-as-the-shirt-or-blazer socks and smooth black shoes. To top this all off; wear a bowtie or white pochet (specially folded white ‘handkerchief’ in pocket on the chest of the jacket).
Women wear a evening gown. This may be long or short, but when followed by dinner a long dress is your go-to-option. Keyword with this dresscode is elegance. You don’t want to appear as to inviting, so cover up that cleavage. Long gloves and goregous (high) heels will complete your outfit. Spend a proper amount of time on refining your like; color your nails and make sure your make-up is done to the last detail.