DEFINITION of 'Purchasing Power Parity-PPP'. An economic theory that estimates the amount of adjustment needed on the exchange rate between countries in order for the exchange to be equivalent to each currency's purchasing power.
Thomas Edison's most famous invention, the lightbulb, paved the way for modern life.
Thomas Edison. Thomas Edison was one of the most productive inventors in American history. With 1,093 U.S. patents (documents granting rights of ownership and design to a specific person) and more in the United Kingdom, France, and Germany, no other inventor has come close to Edison's output.