Generally, the term is used to describe a financial instrument which contains a promise by the issuer, normally a company, to pay the holder of the instrument a defined amount on or by a specified date (this date is when a debt security is said to "mature"), usually with interest. Eurobonds, medium term notes and euro commercial paper are all examples of debt securities.

For the purposes of the Listing Rules and chapters 2 and 3 of the Disclosure Rules and Transparency Rules, debentures, debenture stock, loan notes, loan stock, bonds, certificates of deposit or any other instrument creating or acknowledging indebtedness.

For the purposes of the Financial Services and Markets Act 2000, chapters 4, 5 and 6 of the Disclosure Rules and Transparency Rules and the Transparency Directive (2004/109/EC), bonds or other forms of transferable securitised debts, except securities which are equivalent to shares in companies or which, if converted or if the rights conferred by them are exercised, give rise to a right to acquire shares or securities equivalent to shares.