And this is even more true of short-term instruments such as the overnight Fed Funds rate than it is of a longer term bond rate, because as a general rule, the shorter the duration, the lower the risk.

FORBES: What Is the Liquidity Premium? What Does It Mean?

In that talk, he ostensibly outlined all of the tools available to the Fed if the overnight (Fed Funds) rate hit zero.

FORBES: Peeking Into Ben Bernanke's Bag Of Unconventional Monetary Weapons

The Fed cut its target on federal funds, the overnight interbank loans that form the floor rate for U.S. lending, to just 0.25%, down 75 basis points from the previous 1.0% level.

FORBES: Magazine Article

The Fed funds rate is money loaned from one bank to another overnight.

NPR: Will Fed Rate Cut Help Stem a Recession?

In mid-August the Fed supplied enough liquidity to hold the effective federal funds rate, an overnight interbank rate, below its then target of 5.25%.

ECONOMIST: Central banks have played a starring role

Last month the Fed cut the federal funds rate (applied to money that banks lend to each other overnight to meet reserve requirements) by 1.25 percentage points, to 3%, in just eight days--the biggest one-month reduction in 25 years.

FORBES: Why Your Wallet Feels Thinner

The Fed said it was cutting the federal funds rate, the interest that banks charge each other on overnight loans, to 3.5 percent, down by three-fourths of a percentage point from 4.25 percent.

NPR: Fed Sends Signal with Deep Cut to Interest Rate