An A-line skirt is a skirt

Skirt

A skirt is a tube- or cone-shaped garment that hangs from the waist and covers all or part of the legs.In the western world, skirts are usually considered women's clothing. However, there are exceptions...

 that is fitted at the hips and gradually widens towards the hem, giving the impression of the shape of a capital letter A. The term is also used to describe dress

Dress

A dress is a garment consisting of a skirt with an attached bodice or with a matching bodice giving the effect of a one-piece garment.Dress may also refer to:*Clothing in general*Costume, fancy dress...

es and coat

Coat (clothing)

A coat is a long garment worn by both men and women, for warmth or fashion. Coats typically have long sleeves and are open down the front, closing by means of buttons, zippers, hook-and-loop fasteners, toggles, a belt, or a combination of some of these...

s with a similar shape.
The term was first used by the French couture

Haute couture

Haute couture refers to the creation of exclusive custom-fitted clothing. Haute couture is made to order for a specific customer, and it is usually made from high-quality, expensive fabric and sewn with extreme attention to detail and finished by the most experienced and capable seamstresses,...

 designer Christian Dior

Christian Dior

Christian Dior , was a French fashion designer, best known as the founder of one of the world's top fashion houses, also called Christian Dior.-Life:...

 as the label for his collection of spring 1955. The A-Line collection's feature item, then the "most wanted silhouette in Paris", was a "fingertip-length flared jacket worn over a dress with a very full, pleated skirt".