The sensitivity of a bond to a general change in interest rates is usually captured by assuming that the bond price changes in response to a change in its yield, which is driven by the general level of rates. The responsiveness of a bond price to a yield change is captured in two ways: duration and basis point value.
Duration is a measure of the size and timing of the cash flows paid by a bond. It quantifies these factors by summarizing them in the form of a single number, which is interpreted as an average maturity of the bond. To speak in terms of an average maturity of a bond of a given specific maturity sounds somewhat strange, but remember that a coupon bond is really just a combination of zero-coupon bonds. The average maturity of these component zero-coupon bonds is the duration. The average is not an ordinary average but a weighted average, with the weights based on the present values of the respective cash payments on the bonds. Hence, the weights are not equal, and the large principal repayment places the greatest emphasis on the final payment.