Duration is roughly the time it takes to pay back the original principal.

 

The longer the duration, the more back loaded the cash flow, and the cheaper the bond.

 

Zero coupon bond is the cheapest and has the longest duration.

 

Duration is about change in price in dollar for 1% change in interest rate

 

That is, the longer the duration, the higher the volatility. In a declining rate environment, longer duration is preferred since bond value increases at a faster rate.