about cocktail dresses

Generally, cocktail dresses or cocktail gowns are women's attire
worn at cocktail parties or "black tie" occasions.

The length of cocktail dresses varies depending on fashion and local custom. The length ranges from just above the knee to touching the ankle. When it is about 5 cm  above the ankle it is called tea length and when it is almost touching the ankle it is called ballerina length, although ballerina length dresses usually fall into the evening dresses category.