Spot rate:
spot rate是零息债券的到期收益率，强调债券中间没有现金流量，远期利率是现在决定的，但是开始时间是未来的利率，理解为现在决定的，但是借贷在未来的利率。
the relation between maturity and Treasury spot rates is called the Term Structure of Interest Rates.
Current Yield
Coupon Rate
Accrued Interest
Yield to Maturity(YTM)
Present Value
