A yield is the measure of the return of a bond and allows you to compare the returns of different types of bonds. The most common types of yield are purchase yield and running yield.
The purchase yield, or yield to maturity, measures the return an investor will receive if they buy and hold the bond to maturity. It takes into account the purchase price of a bond, estimated interest payments over the lift of the bond and the return of face value at maturity.
The running yield measures the return an investor will receive as income from coupons. It takes into account the estimated interest payments in relation to the purchase price.