An evening dress (or evening gown) is worn to a formal engagement or affair and is a long flowing garment. It is of course a type of dress which can range in length from a ballerina type dress to a full length evening dress. An evening dress is usually made from luxurious fabrics such as satin, chiffon or silk, and compliments men's black tie formal wear.
Evening dresses for a white-tie events apply the same as black-tie events, but you may also consider a cocktail dress depending on the event.
If accompanying a gentleman who is wearing a kilt, the lady should wear an evening dress with a tartan sash, but you may wear a longer kilted skirt and jacket if desired.