1. In microeconomics, a timescale over which some variables relevant for an economic decision cannot be changed, but which could be changed given more time. In the short run, for example, a firm can buy more materials or fuel, and can hire more unskilled workers, but does not have time to build new plant or to recruit and train more skilled workers or managers. The short run is contrasted with the medium run, in which more things, but not everything, can be changed, and with the long run, in which everything can be changed that can ever be changed at all. Thus, the optimum achieved in a short run can only be as good as the one achieved in the long run.

2. In macroeconomics, short run is associated with the business cycle, or the fluctuations of economic variables about the trend, whereas the trend is associated with the long run. See also trend-cycle decomposition.