By TheStreet Staff Investing in bonds is like ordering a cheese pizza: They’re plain, reliable, and maybe even a bit boring. While fixed-income investments like bonds can help to diversify your portfolio and provide balance during market volatility, bond investing also comes with its own set of complex and somewhat confusing terminology. And because bond prices move in the opposite direction of interest rates, many investors are often left scratching their heads. But once you understand a few basic metrics, like bond duration, you will find bonds to be a pretty straightforward investment—one t…