What is the meaning of Advanced Refunding?

Advanced Refunding is the technique of replacing one bond issue by another. This typically occurs when a municipality can borrow at more favorable terms than the outstanding issue. The new issue's proceeds are used to purchase government obligations which are held in escrow. The income and/or appreciation of these government securities is then used to service the outstanding debt. The escrow may be held until the first call date or maturity of the initial bond issue. If the escrowed funds retire the original issue at the first call date then the issue is pre-refunded. This retirement and replacement process of debt is also known as defeasance.