The McDonald's product used for the Big Mac Index is the Big Mac.
The Economist introduced the Big Mac Index in 1986 as an informal way to compare purchasing-power differences between countries. It uses the price of the same standardized McDonald's hamburger in different markets as a simple illustration of exchange-rate relationships.
The index is not an official measure of national economic performance. Prices can reflect local wages, rents, taxes, supply chains, competition, and differences in product preparation. Even so, the Big Mac's broad international availability makes it a memorable reference point for explaining purchasing power and currency valuation.
The Big Mac became suitable for this role because it was a strongly branded, widely recognized product rather than an obscure local menu item. The index added an economic meaning to a sandwich originally developed by franchisee Jim Delligatti and introduced by McDonald's in the 1960s.