What is meant by Black-Tie?

A black-tie event is a formal social event such as a party at which people wear formal clothes called evening dress. Black tie is one of formal even dress code too, evening occasion like company events. Black tie is a formal dress code for a social gathering that starts at 6:00 pm.
For men this meant to wear tuxedos and for women floor-length gowns. If someone is wears black tie, it means they are wearing formal evening dress, can wear with a jacket or tuxedo.
As per reading, For some Western dress code Black ties is a semi -formal for evening events, originating in British and American conventions for attire in the 19th century. British ENGLISH, the dress code is often referred as a principal element for men every formal event

How should I dress for a black-tie event?

In a gathering where Black tie is required, remember that our suit should always be dark color like (navy, Black or charcoal then pair it with a necktie or a bow tie. dark at a black-tie optional event to approximate the formality of the black tuxedos you'll be seeing. But wearing a black suit to a black-tie optional event is an acceptable choice also. To achieved a perfect fit Tuxedo, suit or dress in this kind of event I recommend you to have a bespoke clothes! Check ---> Ambassador & Smart Fashion. A house of professional bespoke clothes. The best Tailor in Bangkok since 1970's.
Suit plus white shirt and a Black tie is really a good match for an evening function. While the details of black-tie formal wear apply more to men than to women, it's still important to understand that your attire should definitely appropriate in the event or gathering you attended.