A number of brokers, including many binary options brokers, offer bonds in the form of contracts-for-difference, or CFDs for short, for their clients to trade. This means that this asset class is not available as an underlying asset for binary options, like currencies and stock indices often are. Instead, it is offered to traders who prefer to trade in the traditional way with CFDs.
Bonds are essentially debt instruments that are categorized into either corporate bonds or government bonds. It is mainly government bonds that are offered by binary options brokers and other types of brokers. Investors and traders generally consider these among the safest assets in the world, and they are therefore often used to lower the overall risk in an investment portfolio.