Federal Reserve Chair Janet Yellen testified on Capitol Hill Wednesday and dropped an unusual phrase in her commentary: appreciably. 

"The Committee currently anticipates reducing the quantity of reserve balances to a level that is appreciably below recent levels but larger than before the financial crisis," she said.

The Fed's balance sheet is currently at $4.5 trillion. Danielle DiMartino Booth, author of Fed Up: An Insider's Take on Why the Federal Reserve Is Bad for America, doesn't think the Fed will reduce its balance sheet below $2 trillion, if it reduces it at all.

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