Short for venereal disease — an illness passed from one person to another through sex. The meaning is straightforward, but the word itself needs care, because it is old-fashioned in a way that matters. VD was the normal term for decades, on wartime posters and in old health leaflets, and because of that history it now sounds heavy with shame and blame. Doctors and health services stopped using it; today they say STD (sexually transmitted disease) or, more current still, STI (sexually transmitted infection) — infection rather than disease, because a person can carry one without feeling ill. So if you are speaking or writing now, use STI or STD. Where you will still meet VD is in older books and films, in the speech of older people, and sometimes as a rough insult, which is exactly why a learner should recognise it but not reach for it. Say it letter by letter: vee-dee. One more thing: on a menu or a wine list, and in some other contexts, the same two letters stand for something completely different, so read the sentence around it.