A certificate that allows the stated payee to receive cash on-demand, usually issued by governments and banking institutions. A money order functions much like a check, in that the person who purchased the money order may stop payment.

Money orders are readily accepted and converted to cash, and are often used by people without access to a standard checking account. Money orders are an acceptable form of payment for small debts, both personal and business, and can be purchased for a small service fee from most institutions.

Money orders were first issued by American Express in 1882, and later became popularized as traveler’s checks.

Source:  investopedia.com