postal order
noun [ C ] UK uk/ˈpəʊ.stəl ˌɔː.dər/ us/ˈpoʊ.stəl ˌɔːr.dɚ/ (US money order)
邮政汇票
an official piece of paper with an amount of money written on it that you can send or give to someone who can then exchange it for the same amount of money at a post office