"Dolphin shorts, or Dolfins, are a specific style of unisex shorts for athletics. They are typically very short and were originally made from nylon with contrasting binding, side slits, and rounded corners, with a waistband at the top—a style popular [in the US] in the 1980s.

The name is from Dolfin, the American company that first produced this style of shorts in the 1980s. Due to their shortness, they are sometimes identified as a form of hotpants."

Source: Wikipedia
https://en.wikipedia.org/wiki/Dolphin_shorts