Junior debt is debt that is either unsecured or has a lower priority than of another debt claim on the same asset or property. It is a debt that is lower in repayment priority than other debts in the event of the issuer's default. Junior debt is usually an unsecured form of debt, meaning there is no collateral behind the debt.

In the event that the issuing company goes out of business, the junior debt has a smaller probability of being paid back, either with money or with assets, since all higher-ranking debt will be given priority. Junior debt is also called subordinated debt, due to its position in the debt hierarchy. One common junior debt is the seconds mortgage which ranks behind the first mortgage and has a lesser claim in the event of default.