There are many parties and events which require guests to dress up in a particular theme or dress code, and for most of the formal events, black tie has been, and still is, a popular choice.
Women have a relatively wider choice, as the attire can either be a three quarter length or floor-length evening gown. Even a short, dressy cocktail dress (depending on the time of the occasion) looks good when paired with the right jewelry, a hand bag or a clutch of either silk, satin, velvet, or brocade, and a suitable pair of sandals or pumps.
Black Tie Preferred
This dress code is used in the invites when the host expects the guests to wear a dark suit and a tie, if not a tuxedo, to the event. This option was introduced keeping in mind people who genuinely could not afford to own or rent a tuxedo, or those who did not want to spend too much money on one.
Black Tie Invited or Optional
Both these terms mean the same thing. Unlike the first two, here the host does not insist on men wearing tuxedos. They can either choose to wear tuxedos or wear a dark suit, preferably black or dark gray, with a white dress shirt; and instead of a bow tie, a necktie can do. It is better to opt for silk neckties with solid colors instead of patterns.
A solid-colored tie gives it the look of an ensemble for a formal event or occasion. As the term suggests, this dress code gives men an option of choosing between typical formal wear, a tuxedo, or a simple formal suit.
When you are invited to a party with a black tie optional dress code, your choice of attire widens and there are more options for you to choose from. Thus, it is the most flexible among the black tie dress codes.