This isn't really accurate, because it would describe any "expansionary" monetary policy. QE involves adding liquidity (i.e. cash) to the financial system direc

This isn't really accurate, because it would describe any "expansionary" monetary policy. QE involves adding liquidity (i.e. cash) to the financial system directly when interest rates are already low and so the normal tools (open market operations and to a lesser extent the discount rate) are ineffective. QE thus typically involves very large expansion of the Fed's balance sheet (the assets are the securities they buy, and the liabilities are the cash issued), compared to small fluctuations when they are using OMO. The ultimate effect is an increase in the money supply just like normal expansionary Fed operations, just through different means. Also QE1 and QE2 involved the Fed buying "non-traditional" assets like mortgage-backed securities that were toxic at the time and some of which "fade away" over their lifetimes (e.g. an MBS is not worth anything once all of the loans composing it are paid).