showgirl skirt
A skirt or dress that only covers the sides and rear, but leaves the front open. Usually worn with something like a leotard or swimsuit bottom.
If the skirt isn't stand alone, but is worn over another skirt, shorts or pants, it's an overskirt instead. Overskirt and showgirl skirt are mutually exclusive.
If the fabric also covers the front like a regular skirt, use high-low skirt instead.
