What does it mean to say that there is a bubble in the housing market?

What does it mean to say that there is a bubble in the housing market?

1. What does it mean to say that there is a bubble in the housing market? Briefly describe the effect that the bursting of the housing bubble had on the U.S. economy.
2. How can an investment bank experience a “run”? Briefly describe the effect the runs on Bear Stearns and Lehman Brothers had on the U.S. economy.
3. Briefly discuss the policy actions the Federal Reserve and the Treasury took during the financial crisis.