What is Lost Sales?

Legal Definition
Lost sales, also referred to as lost revenue, income or profit, is a term used in the context of Internet piracy to refer to sales that did not occur because potential customers have chosen not to buy a product but to obtain it from an illegal source for a lower cost or for no cost. Figures for lost sales usually assume that consumers who use pirated content would always choose to purchase the product at the market rate, if the illegal sources were not available.

The content industry has endorsed studies concluding that the value of lost sales amounts to billions of U.S. dollars. However, other scholars and free culture and copyleft activists argue that the industry figures are grossly inflated, because some individuals who obtain pirated copies would not have purchased the content, even if the opportunity for piracy did not exist.
-- Wikipedia