The action taken to stimulate an economy, usually during a recessionary period, through government spending, and interest rate and tax reductions. The term "pump priming" is derived from the operation of older pumps; a suction valve had to be primed with water so that the pump would function properly. As with these pumps, pump priming assumes that the economy must be primed to function properly once again. In this regard, government spending is assumed to stimulate private spending, which in turn should lead to economic expansion.

The phrase originated with President Hoover's creation of the Reconstruction Finance Corporation (RFC) in 1932, which was designed to make loans to banks and industry. This was taken one step further by 1933, when President Roosevelt felt that pump-priming would be the only way for the economy to recover from the Great Depression. Through the RFC and other public works organizations, billions of dollars were spent "priming the pump" to encourage economic growth.

The phrase was rarely used in economic policy discussions after World War II, even though programs developed and used since then, such as unemployment insurance and tax cuts, are automatic pump primers of sorts. However, during the financial crisis of 2007/2008 the term came back into use, as interest rate lowering and infrastructure spending was thought to be the best path to economic recovery.