Keynesian refers to the economic theories of British economist John Maynard Keynes, which argue that active government intervention, particularly through fiscal policy, can stabilize the economy by managing aggregate demand. Keynesian economics suggests that during a recession, the government should increase spending or cut taxes to stimulate demand, and in a boom, it should reduce spending or raise taxes to cool the economy and prevent inflation. Key principles include the importance of aggregate demand, the multiplier effect, and the idea that prices and wages can be "sticky," causing markets to not always self-correct quickly.