A written, unconditional order by the drawer to the drawee to pay a certain sum, either immediately or on a fixed date, for payment of goods or services received. The drawee accepts the bill by signing it, thus converting it into a post-dated check and a binding contract. A bill of exchange is also called a draft but, while all drafts are negotiable instruments, only "to order" bills of exchange can be negotiated. A bill of exchange is the most often used form of payment in local and international trade, and has a long history- as long as that of writing