Debt is an obligation that a person or organization has to another person or organization. Debt may be in the form of a bond, note, mortgage, line of credit, or other financial instrument. Debt may be secured by assets, which means that the assets will be seized in the event of default, or be unsecured.
Further it is not mandate that there should be any documents of proof. If there is any document then this debt would be secured debt otherwise unsecured debt.
Now come up to legally enforceable debt, if someone has a legal right or any particular law to recover the particular debt then it is said legally enforceable debt.The best example is section 138 of NI Act, which governs the enforceability of debt, which is secured by Cheque.