Yield elasticity of bond value is the percentage change in bond value divided by a one per percentage change in the yield to maturity of the bond. This is equivalent to saying the derivative of value with respect to yield times the (interest rate/value). This is equal to the MacAulay Bond Duration times the discount rate, or the modified bond duration times the interest rate.

If elasticity is below -1, or above 1 if the absolute number is used, it means that the product of the two measures, Value times yield or the interest income for the period will go down elasticity