The yield-to-maturity is the yield of a bond assuming that the bondholder were to buy and hold the security until the maturity date. The calculation is based on the interest rate, length of time, and price paid, and assumes coupons could be reinvested at the same yield.
For example, suppose that a municipality issues a non-callable 10-year $1,000 par value general obligation bond that pays 3% per year. The yield-to-maturity would tell an investor what he or she would earn if the bond was purchased at the current market price and held until maturity.