E-mail Article | Print Article | digg it | Del.icio.us. http%3a%2f%2fwww.morningstar.com%2fInvGlossary%2fGlossary.aspx%3fterm%3dcoupon_rate_definition_what_is. Coupon Rate. The annual interest rate of a debt/bond security that the issuer promises to pay to the holder until maturity.