A measure of the expected volatility of a bond fund in response to interest rate fluctuations. The time to maturity impacts the sensitivity of any given bond. For example, the effects of a shift in interest rates would be five times greater for a 10 year treasury bond than a 2 year treasury bond. As interest rates go up, the duration shortens and the bond is expected to decrease in price. With bond funds, the effective duration for many bonds with different maturity dates and yields within the fund is averaged.