The term 'skirt shape' can refer to two different types of skirts: an A-line skirt and a HOOP skirt. An A-line skirt is a type of skirt that is fitted at the waist and gradually widens towards the hem, creating an A-shaped silhouette. A HOOP skirt is a type of skirt that is supported by a frame made of metal or plastic hoops, creating a bell-shaped silhouette. Both of these skirt shapes are popular choices for formal occasions.