The document defines marketing margin as the difference between the price a company pays to purchase a product and the price it charges customers to resell the product. Marketing margin accounts for the costs of equipment, transport, labor, capital, risk, and management involved in marketing the product. It is similar to, but distinct from, profit margin. The document provides an example calculation of marketing margin using the prices of milk (raw material) and cheese (finished product). Companies use marketing margin to assess profitability and ability to respond to competition. However, it has limitations and does not account for business growth or fluctuating margins over time.