An IUD is a piece of plastic or metal which is put inside a woman's womb in order to prevent her from becoming pregnant. IUD is an abbreviation for `intra-uterine device'. = coil. intrauterine device. intra-uterine device a small plastic or metal object used inside a woman's uterus (=place where a baby develops) to prevent a baby being born = coil (intrauterine device)