A style of tightfitting men's swimming costume cut like underwear briefs that covers the buttocks and groin but not the legs and reveals the bulge of the genitals; especially worn in surf lifesaving and in swimming races.
swim trunks
noun
Synonym of swimming trunks
How often have the words budgie smugglers and swim trunks occurred in a corpus of books? (source: Google Ngram Viewer )