[1] There are three principal cost functions (or 'curves') used in microeconomic analysis: The idealized "long run" for a firm refers to the absence of time-based restrictions on what inputs (such as factors of production) a firm can employ in its production technology.
The long-run cost curve does not try to anticipate changes in the firm, the technology, or the industry.
For example, if a micro-enterprise wanted to make a few pins, the cheapest way to do so might be to hire a jack-of-all-trades, buy a little scrap metal, and have him work on it at home.
However, if a firm wanted to produce thousands of pins, the lowest total cost might be achieved by renting a factory, buying specialized equipment, and hiring an assembly line of factory workers to perform specialized actions at each stage of producing the pins.
However, many economic models assume that cost curves are differentiable so that the LRMC is well-defined.