Corporate bonds are debt issued by companies. They pay a fixed coupon each year and then repay the principal at the end of the term, so if you buy a 6% 10 year bond, you get a 6% payment each year and your money back at the end of the ten years.
As far as I can see, it is quite difficult to buy them without using a fund. An example of a fund would be:
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Note that the risk of corporate bonds increases in recessionary times as teh chances of the company that issues them goes bust. This is why the yields (the difference between the price you pay for the bonds and the coupon) increase. Currently for short-term General Motors bonds you can get yields in the 30-100% range! (It means the perception in the bond market is that the company is about to go bust!). So I wouldn't go all in on them! There is also the danger that a company that was previously rated as investment grade (A- or above, I think) is downgraded to junk (BBB) or just to a lower investment grade. This will result in a loss if you have to sell the bonds before the term is due, but shouldn't make a difference if you hold them to maturity (assuming the company doesn't go bust).
Disclosure: No connection with Rabo and no investments in corporate bonds at the moment. Strictly small amount amateur investor - nothing I say should be taken as advice!