Equilibrium
With respect to supply, time plays a role that it does not (in most cases) play in the case of demand. If there is plenty of time for the suppliers to adjust to a change in the price, we have a long run analysis. This means the sellers can invest and expand productive capacity, in response to a high price, or can gradually reduce the productive capacity by under-replacing worn-out equipment in the case of a low price. However, if the sellers are not sure the high or low price will continue for a long time, a short run analysis may be more appropriate. In a short run analysis, we treat the plant and equipment of the industry as inflexibly given. In that case, output can be increased only by using that fixed plant and equipment more intensively. Thus, we would expect the adjustment of supply to a change in price to be more complete in the long run than in the short run.
We do not ordinarily apply the long run versus short run distinction to demand, but there are some special cases where it might be important. For example, for durable goods such as cars, buyers might adjust less completely in the short run than in the long, since they can postpone replacement of their durable goods until the price comes down. In the long run, the goods wear out and so the consumers cannot postpone replacement long enough.
In summary,
Equilibrium
