External debt - IMF
The provision of economic value by the creditor, or the creation of debt liabilities through other means, establishes a principal liability for the debtor, which, until extinguished, may change in value over time. For debt instruments alone, for the use of the principal, interest can, and usually does, accrue on the principal amount, increasing its value.
International Monetary Fund (IMF), "External Debt Statistics: Guide for Compilers and Users; Appendix III. Glossary of External Debt Terms", Washington D.C., 2003