Final answer:
The long run is the period in which all costs are variable for a firm. During this time, no costs are fixed and the firm can make decisions related to production technologies or processes.
Step-by-step explanation:
The long run is the period of time when all costs are variable. In a firm, the long run depends on the specific circumstances of the business and is not a precise period of time. For example, if a firm has a one-year lease on a factory, then the long run is any period longer than a year, as they are no longer bound by the lease after that time.
In the long run, no costs are fixed, which means that a firm can build new factories, purchase new machinery, or even close existing facilities. During the long run, the firm will typically compare different production technologies or processes to determine the most efficient and cost-effective options.