short pants

Short pants is the dated North American term for what most of the English-speaking world simply calls shorts or short trousers. The phrase carries a slightly old-fashioned or nostalgic flavour, evoking images of mid-20th century children's clothing and school uniforms. Today it mostly appears in period contexts, older speakers' vocabulary, or ironic usage — as in calling an adult out for wearing them as if they're still a kid. In contrast, British English has always preferred the term 'short trousers'.