This is a historic week for us. Our national debt will now exceed 100% of Gross Domestic Product. Mathematically speaking, we are hosed.
A liquidity trap occurs when a government can no longer stimulate it's economy. And since our government uses Keynesian theory I suppose the Keynesian definition is appropriate. http://en.wikipedia.org/wiki/Liquidity_trap
Japan's debt has exceeded 100 and 200% of GDP for 21 years. They have one thing going for them that we don't. Their citizens pick up the country's debt tab through individual investment. They get a small interest return. We sell our debt to the world, we also pay them the interest.