The difference in yield, at a given time, between two bonds or between different segments of the bond market. For example, the yield spread between AAA-rated bonds and A-rated bonds may be one half of 1% at a particular time. Likewise, the yield spread between long-term taxable and nontaxable bonds may be 2%. Yield spread may be caused by any of various factors, including maturity difference, risk difference, or taxability difference.