If the Invitation says "Black Tie"
Black Tie" events require dressing formally in a tuxedo. Today, "Black Tie" means to dress in tuxedo and tuxedo accessories, not specifically to wear a black tie. Matching your tuxedo jacket and pants with the right tuxedo shirt, tuxedo vest, and cuff links add to your tuxedo style. Formal evening wedding invitations might be Black Tie.
If the Invitation says "Black Tie Preferred"
Indicates that the host prefers guests to wear formal evening attire.
Black Tuxedos, White Dinner Jacket (mid-April through Labor Day)
or a dark contemporary style Tuxedos are acceptable (no Tailcoats).
Non-formal Dress Suits are also acceptable, but not preferred by the host.
If the Invitation says "Black Tie Optional"
Is not as strong a statement for formal attire as "Black Tie" or
"Black Tie Preferred," yet formal dress is wholly appropriate and
acceptable. Styles may include Black Tuxedo, White Dinner Jacket
(mid-April through Labor Day) or a dark contemporary style Tuxedo
(no Tailcoats).
If the Invitation says "Black Tie Invited"
Is a phrase appearing more frequently than "preferred" or "optional."
It is usually in the context of large gatherings of civic or business
groups, such as a dinner sponsored by the Chamber of Commerce. It
states that gentlemen attending are welcome to dress formally if
they would like, but it is not required. Styles for these affairs
are the same as for "Black Tie Optional."