It's a combination of loans. The idea is let's say I have 100 identical loans I made (in reality, there are averages). Further, we agree 5-15% are likely to default. I'm going to get paid 85-95% of the interest + principle. But I want that money now. You want to invest in future cashflow, so I want to sell you a loan. Buying one from me is kinda risky, you may get back 100% or 0% of the interest + principle you expect. So instead I sell all 100 as a lump sum, and you and 99 other people each get 1%.
But, CDOs go a step further. You may have more or less risk tolerance. So we chop it up. You can buy something that gets paid back if 70% of the loans are good, or only if over 70% or over 80%, or even over 90%. The less likely you are to get paid back, the more you make.
So the person who absolutely wants to get paid back gets a small interest rate. The person who only gets paid back if literally every loan pays off gets a much higher rate.
In 2008, what happened is all those people buying the "very safe" 75-85% failure rate sections also were getting wiped out.
But, CDOs go a step further. You may have more or less risk tolerance. So we chop it up. You can buy something that gets paid back if 70% of the loans are good, or only if over 70% or over 80%, or even over 90%. The less likely you are to get paid back, the more you make.
So the person who absolutely wants to get paid back gets a small interest rate. The person who only gets paid back if literally every loan pays off gets a much higher rate.
In 2008, what happened is all those people buying the "very safe" 75-85% failure rate sections also were getting wiped out.