bond=债券

Class AAA = risk free , normally the issuer is the government (you still have inflation risk, political risk, etc)

Class AA, A, BBB, BB = investment grade bond, relatively safe.

generally, a bond is a promise to repay the principal and the coupon (interest) at the end of maturity

all bonds are required to repay the principal

some government bonds donot have interest but sold on a discounted price

face value will approach par value when the bonds approach maturity

Unrealized gain/loss = if you sell now, the difference compare to the money you get at the end of maturity