If you are lucky, you may receive a formal invitation with the words black tie printed at the bottom. This is an indication of a dress code. Men who attend a black tie occasion are expected to wear dinner jackets, worn with the conventional black bow tie. Women at such an event are expected to wear the female equivalent – a formal, often long, evening gown.
At an even more formal event, the dress code expected may be white tie. Again, this is a bow tie – a white bow tie. This time the convention is that the men wear tail coats. Again, women are expected to wear the equivalent – which is more variable according to fashion.