The collateral is usually preferred to be liquid, such as an irrevocable letter of credit, but some sureties will also take other pieces of collateral, such as certain equipment or even real property. A Collateral Bond is different when used in the context of a surety bond.
A debenture is a type of bond or other debt instrument that is unsecured by collateral. Since debentures have no collateral backing, they must rely on the creditworthiness and reputation of the issuer for support. Both corporations and governments frequently issue debentures to raise capital or funds.