汇票是一种票据，它是一种委付证券，基本的法律关系最少有三个人物，发票人、执票人与付款人。发票人签发汇票给执票人，并委托付款人向执票人付款。

《中华人民共和国票据法》给汇票如此定义：“汇票是出票人签发的委托付款人在见票时或者在指定日期无条件支付确定的金额给收款人或者持票人的票据。”

根据出票人的不同可以将汇票分为银行汇票和商业汇票。目前中国大陆能够签发商业汇票的仅限于具有法人资格的工商企业和事业单位。汇票还可以分为即期汇票和远期汇票。前者是指见票即付的汇票，后者是载明一定时间或特定日期付款的汇票。远期汇票有三种。一种是定日付款的汇票，称为定期汇票或者定日汇票、板期汇票；一种是出票后定期付款的汇票，称为记期汇票；还有一种是见票后定期付款的汇票，称为注期汇票。

A postal order is a financial instrument usually intended for sending money through the mail. It is purchased at a post office and is payable at another post office to the named recipient. A small fee for the service, known as poundage, is paid by the purchaser. In the United States, this is known as a postal money order. Postal orders are not legal tender, but a type of promissory note, similar to a cheque.