An operation on a man in which the small tube carrying sperm is cut or blocked, so that he can still have sex normally but cannot make a woman pregnant. It is a permanent method of birth control, usually chosen by men who already have the children they want. It is quick and done under local anaesthetic — most men walk out the same day — and it does not change a man's hormones, his desire, or his ability to have sex, which is the thing people most often wrongly worry about. The usual verb is 'have': 'he had a vasectomy'. A doctor 'performs' one. You may also hear the informal verb 'get snipped' or 'have the snip' in British English — friendly, slightly joking, and very common between friends. Reversing a vasectomy is possible but often fails, so in normal talk it is treated as a final decision. In Taiwan and elsewhere this is a normal medical word; it is not rude, but like anything about private body parts, people choose when to say it.