Quantitative easing (QE) is also referred to as 'printing money' and historically known as 'debasement of money'.

In the modern world QE is a monetary policy action whereby a central bank purchases government bonds or other financial assets in order to stimulate economic activity.

The central bank uses newly created money in order to purchase the assets, thereby increasing the total money supply in existence and (theoretically) devaluing all previously existing money in circulation.