Definition: Debt instrument
External debt - IMF
Existing debt instruments typically arise out of contractual relationships under which an institutional unit (the debtor) has an unconditional liability to another institutional unit (the creditor) to repay principal with or without interest, or to pay interest without principal. These instruments include debt securities, loans, trade credit, and currency and deposits. Debt instruments may also be created by the force of law—in particular, obligations to pay taxes or to make other compulsory payments—or through rights and obligations that results in a debtor accepting an obligation to make future payment(s) to a creditor.
International Monetary Fund (IMF), "External Debt Statistics: Guide for Compilers and Users; Appendix III. Glossary of External Debt Terms", Washington D.C., 2003