A bond that is likely to increase in value in a bull market, when interest rates are declining. Most bonds tend to increase in value when interest rates decline, but bull bonds refer to types of bonds that do especially well in this environment.

|||A common example of a bull bond is the principal only (PO) strip mortgage-backed security. Whereas most bonds will increase in value in a declining rate market, mortgage-backed securities perform especially well. POs are mortgage securities created by separating principal payments from interest payments collected in a pool of mortgage securities. The principal payments are then combined to form a mortgage pool. PO mortgage securities do well in a falling rate market because mortgage holders refinance their loans at lower interest rates. Investors are repaid their original investment more quickly, increasing the rate of return for the mortgage-backed security.