A loincloth is a piece of cloth wrapped around the hips to cover the private parts, and that is more or less the whole garment. It is not trousers, not shorts, and not the underwear you buy in a shop. In very hot places, and in many older ways of life, men — and in some cultures other people too — wore this for work, for ritual, or for everyday heat. You still meet it in some communities, in dance, in film, and in history books. English speakers usually say it about other times and other places, not about what they themselves put on for the office, so it can sound like an anthropology-word, a little distant. “Loin” here is the old body-word for the area between the ribs and the top of the legs, the same loins you hear in old Bible English.