“You can’t prevent some of the losses that are occurring,” said Nellie Liang, a senior fellow at the Brookings Institution and a former director of financial stability for the Fed. “You want to make sure that at the end of the period where the economy is affected by this crisis and shut down, that you haven’t left everyone in such a bad place that you can’t recover quickly.”

The basic problem the Fed is trying to solve is that financial markets — particularly the bond market, where investors trade government and corporate debt — have nearly frozen up in recent days. Since no one is sure how bad the pandemic will be or how long it will last, investors are wary of buying any bonds, even ones that would normally be seen as safe havens. By promising to buy debt, the Fed is trying to get markets working again.

OK, but what does that mean in the real world?

Broadly speaking, American businesses right now fall into two groups. In the first category are companies, like airlines, hotel chains and cruise ship operators, that have seen their revenue more or less wiped out by the pandemic. Congress might step in to bail some of those companies out, but there isn’t much that the Fed can do for them.

Instead, the Fed’s actions are focused on the second set of businesses. These are companies that are basically healthy but in danger because of the freeze-up in financial markets. Some have been insulated from the outbreak’s effects but rely on debt as part of their normal operations. Others have lost business because of the virus but could survive if they could borrow to cover their expenses.

If those businesses start to fail, there will be more layoffs and still more business failures — an economic nose-dive that could be harder to pull out of. The Fed is trying to contain the damage and prevent that cascade effect.