The general term for the rate of income from an investment expressed as an annual percentage and based on its current market value. For example, if a corporate bond or gilt originally sold at £100 par value with a coupon of 10% is bought for £100 then the coupon and the yield are the same at 10%, or £10. But if an investor buys the bond for £125, its coupon is still 10% (or £10) and the investor receives £10 but as the investor bought the bond for £125 (not £100) the yield on the investment is 8%.
Corporate bonds are one of the main ways companies can raise money (the other is by issuing shares) by borrowing from the markets at a fixed rate of interest (the reason why they are also known as “fixed-interest securities”), which is called the “coupon”, paid twice yearly. But the nominal value of the bond – usually £100 – can fluctuate depending on the fortunes of the company and also the economy. However it will repay the original amount on maturity.