A bow tie is a type of men's necktie that isn't worn lengthwise, but rather fits in a bow shape across the front of the neck. These ties are strips of fabric that are tied into bows with a center knot and two triangular or rectangular ends. Pre-tied bow ties are sold already tied, but a traditional bow tie is purchased as a length of fabric that the wearer ties to form a bow in front of his shirt.
Black silk bow ties are worn with the black formal men's evening suit known as a tuxedo, or tux for short. Tuxedos are traditionally worn with a white shirt and a black bow tie. Many formal invitations specify the dress is "black tie" and this means a black bow tie. Modern style often permits other colors of ties, but black is still the most common. At weddings, the groomsmen's ties may be in the wedding accent color.
Bow ties are available in many types of fabrics and a wide range of colors from brights and pastels to neutrals. These less formal versions may be in wool plaid or vivid designs or patterns such as polka dots. They are often considered a little eccentric or light-hearted and are usually worn with a shirt and sweater or shirt and vest combination rather than with a suit.