Boardies
From Openwaterpedia
Boardies are a style of men's and women's summer wear and swimwear. They were originally developed for aquatic sports, specifically for surfing, but in more recent years they have grown in popularity outside of these sports, and have become a popular form of general beach and summer wear.
The name of "boardies" originates from "boardshorts" and its affiliation with aquatic sports that use a board, such as surfing and boogie-boarding.
Boardies are especially popular in North America and spread beyond surfing especially as the skater punk fashion trend got underway. They are also typically worn in men's beach volleyball.