This is a market of over $47 trillion dollars. It's insurance that companies will not default on their debts. The problem is that in a normal insurance company there are actuarial calculations based on historical and projected data, regulations, and so on that result in a loss reserve available to pay insured losses. This, on the other hand, is an unregulated market of contracts with no specific loss reserve. It is causing much angst in the markets.
At the center of these concerns is a vast, barely regulated market in which banks, hedge funds and others trade insurance against debt defaults. This isn't like life insurance or homeowners' insurance, which states regulate closely. It consists of financial contracts called credit-default swaps, in which one party, for a price, assumes the risk that a bond or loan will go bad. This market is vast: about $45 trillion, a number comparable to all of the deposits in banks around the world.