a-line means: The A-line silhouette is a triangle-like shape that starts at the waist and gradually becomes wider as you move down from the hips to the hem. The shape is reminiscent of the capital A. Christian Dior first used the term to refer to his 1955 A-line Spring Summer Collection. It was later used by Yves Saint Laurent in 1958 Trapeze Line, his first house collection. The shape is now below the shoulder. (in Fashion Dictionary)

What else does a-line mean?

Apparel style that fits the shoulders or skirt just below the waist. The dress gradually flares to create a wider hemline and resembles the letter A. Christian Dior was the first to create an A-line design in 1950. (in Fashion Dictionary)