External debt - IMF
Duration is the weighted average term to maturity of a debt instrument. The time period until the receipt/ payment of each cash flow, such as six months, is weighted by the present value of that cash flow, as a proportion of the present value of total cash flows over the life of the instrument. Present value can be calculated using the yield to maturity or another interest rate. The more the cash flows are concentrated toward the early part of a debt instrument’s life, the shorter the duration relative to the time to maturity.
International Monetary Fund (IMF), "External Debt Statistics: Guide for Compilers and Users; Appendix III. Glossary of External Debt Terms", Washington D.C., 2003