Whale tail is the Y-shaped rear portion of a thong or G-string when visible above the waistline of low-rise pants, shorts, or skirts that resembles a whale's tail. The fashion was popular in the early 2000s and waned within the decade, but has become more fashionable in recent years.
Low-waisted trousers, such as low-rise jeans or hip-huggers, and higher-cut thongs led to greater exposure of the whale tail. The trend was also associated with the trend of sporting lower back tattoos.
The word was selected by the American Dialect Society in January 2006 as the "most creative word" of 2005.