Trunks are the most common men's swimwear in North America. They look similar to shorts worn as clothing on land, but are made from light, fast-drying materials (usually nylon or polyester) and feature a tighter-fitting lining inside the shorts. Colors and inseam lengths can vary widely.
Boardshorts are a longer version of trunks that come to or past the knee. They often have a non-elastic waist and fit closer to the torso. Originally developed for “board sports”(surfing, paddleboarding, etc.) they were designed to have less material that could catch as you mounted your board.