A debt instrument that is issued with a promise of repayment on a certain maturity date at a specified rate of interest. These kinds of securities include bonds, debentures, preferred stock, collateralized securities, promissory notes and zero-coupon securities.
Additional meaning of Debt Security:
Debt securities are safer investments than equity securities, because the principal amount is returned to the lender at the maturity date. Debt securities can be traded between two parties, much of the trading is now conducted electronically.