Bonds are loans issued by entities like governments and corporations to investors. There are several types of bonds: Regular bonds have a fixed coupon and maturity date with no call or put options. Callable bonds allow the issuer to redeem the bond before maturity if interest rates decline. Puttable bonds give the investor the right to sell the bond back to the issuer before maturity if rates rise. Convertible bonds can be converted into equity in the borrowing firm. Perpetual bonds have no maturity date but may have a call option, while tier-2 bonds under Basel III standards have fixed coupons and maturity but a call option.