Yield to maturity

The single discount rate that makes the present value of a bond's cash flows equal its market price. It is the return an investor earns holding to maturity, assuming coupons are reinvested at the same rate.

The reinvestment assumption is the model's weak point and is rarely true, so realised return differs from the quoted yield.

For comparing bonds of different coupons and maturities it remains the standard measure.

Current yield, which is just coupon divided by price, ignores the capital gain or loss to maturity and is a poorer measure.