"Libor" is the London InterBank Offered Rate. Effectively, it's the interest rate at which banks in London borrow from each other. It's an important number because the financial sector uses it to figure out how to price mortgages, loans, bonds, and much else. When it's low, that's a good thing: It means banks feel pretty confident lending to one another. And it's pretty low right now. The three-month rate is at a record low, in fact. And that's good. How good? Brad DeLong says, "Now I am happy. Now I see 'green shoots'."