Speedos are the very small, tight swimming trunks that men wear — the brief kind that look like underwear, not the loose shorts most men swim in at the beach. Speedo began as a brand name of an Australian swimwear company, and the company still makes all kinds of swimwear, including big loose shorts and women's swimsuits. But the plural word Speedos, in everyday speech, has drifted away from the company and now means that one shape, whoever made it. This is the same thing that happened to OK繃 or 舒潔 in Chinese: the brand became the word for the object. Because of that drift, it is usually written with a small s these days — speedos — even though the company would prefer the capital. It is a plural word, like trousers or glasses: a pair of speedos, my speedos are wet. You cannot wear "a speedo" any more than you can wear "a trouser". Now the part that matters more than the definition: this word carries a joke in it. In Britain, Australia and America, a grown man in speedos is a running gag — people call them budgie smugglers in Australia — and saying someone was wearing speedos is often a gentle laugh at him. The exception is sport. Competitive swimmers wear them because loose shorts drag in the water, and nobody laughs at a swimmer at a swim meet. Also worth knowing for travel: many public pools in Taiwan, Japan and Europe actually require this kind of tight trunks and will turn away men in loose beach shorts, so the funny word describes a compulsory item surprisingly often.

（男用）三角泳褲；Speedo 是澳洲泳裝品牌，但講 speedos 通常指那種緊身小三角泳褲本身，不管牌子。台灣泳池常規定要穿這種，海邊那種寬鬆海灘褲反而不能下水。