Business cycles are recurrent sequences of economic activity that occur in market economies. They consist of alternating waves of expansion and contraction that are observed across many different sectors in an economy at about the same time. While expansions are characterized by increasing economic activity in output, income, sales, and employment, recessions are defined by across-the-board decreases in the levels of economic activity. Business cycle phases of expansion and contraction tend to be asymmetrical, meaning recessions are short interruptions of expansion periods of long and sustained growth.