PJ's (also written PJs, pjs, or pj's) is a casual short form of pyjamas — the soft trousers and top you sleep in. People say it at home, in shops, and in ads; it is friendly and a bit childlike, though adults use it too. You put on your PJs, stay in your PJs, live in your PJs on a lazy Sunday. The spelling wobbles because English cannot decide how to write the short form of a word that already has two spellings: British pyjamas, American pajamas. The apostrophe in pj's once marked the missing letters, but many people now write PJs with no apostrophe, the way they write TVs. It is spoken English more than school English; a form will usually say pyjamas or pajamas, not PJs.