The Big Mac Index is an informal measure of purchasing power parity (PPP) between countries. It compares the price of a standard Big Mac burger from McDonald's in different nations to assess whether currencies are undervalued or overvalued. By using a common product, the index provides a simple way to gauge economic conditions globally. Introduced by The Economist in 1986, the index highlights discrepancies in currency values based on local prices. For example, if a Big Mac costs significantly more in one country than another, it may indicate that the first country's currency is overvalued relative to the second.