The document defines key cost terms for a business: - Total cost is the sum of total fixed cost and total variable cost, and increases with output while fixed cost stays constant. - Average cost is total cost divided by units of output and is also called average total cost. - Marginal cost is the addition to total cost for each extra unit of output produced. - The learning curve shows that as a firm's output increases over time, the cost per unit decreases as the firm learns efficiencies in production.