Commercial paper is short-term debt issued primarily by banks and large businesses, often just for a few days. The rate shown here is for "top-tier" companies, or those with the best credit ratings. High rates have made it more difficult for business to obtain the money they need for everyday expenses.
Higher bond yields indicate less willingness to lend to businesses. Yields on junk bonds have jumped, signaling an aversion to risk.
Libor--the London Interbank Offered Rate--is what banks charge one another for short-term loans. It is the basis for many financial contracts--including home mortgages and student loans--and it is a sign of whether banks trust each other. Higher rates mean banks are less willing to lend to one another.
The difference between Treasury bills and a three-month Libor is a measure of stress in the credit markets. By historical standards, the spread has been high all year: it averaged about 25 basis points (0.25%) from 2002 to 2006. Higher spreads are signs of anxiety.
Investors have taken money out of stocks, bonds, and money market funds to buy safe assets, forcing the yield on short-term Treasury bills down. A lower yield indicates greater concern about the financial system.