Short-run: A period of time during which at least one factor of production (usually capital) cannot be changed. Some inputs can be adjusted, but others remain fixed.
Economies of Scale: When a firm experiences cost advantages due to an increase in its scale of production. This often occurs when producing larger quantities reduces average costs.
Diseconomies of Scale: When a firm experiences cost disadvantages due to an increase in its scale of production. This happens when producing larger quantities leads to higher average costs.