Bonds are debt instruments. In contrast to the purchase of a stock, the buyer of a bond does not acquire equity in the company (i.e. an equity right) but instead loans the company money for a certain period of time.
Bonds can carry a fixed or variable interest rate and have a predefined term to maturity and means of repayment. Special forms are e.g. warrant and convertible bonds.
Bonds are fundamentally traded in nominal values. Their prices are expressed as a percentage of the nominal value, e.g. 92.56%.