A fixed-income security is an instrument that allows governments, companies, and other types of issuers to borrow money from investors. Any borrowing of money is debt.
The terms “fixed-income securities,” “debt securities,” and “bonds” are often used interchangeably.
Securitised bonds are created from a process called “securitisation,” which involves moving assets into a special legal entity. This legal entity then uses the assets (such as mortgages, auto loans, student loans, credit card receivables, etc.) as guarantees to back (secure) bond issue, leading to the creation of securities bonds.