The so-called legal bill refers to the bill that conforms to the law. What we usually call bills usually refers to legal bills.

Bills in a broad sense include all kinds of securities and vouchers, such as stocks, treasury bonds, corporate bonds, invoices, bills of lading and so on. In a narrow sense, negotiable instruments refer to the negotiable securities that are issued by the drawer according to law and paid unconditionally by himself or others, that is, some negotiable securities that can replace cash circulation.