money order
noun [ C ] US uk/ˈmʌn.i ˌɔː.dər/ us/ˈmʌn.i ˌɔːr.dɚ/ (UK postal order)
汇票，汇款单
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