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. Arguably the most successful inventor in human history, Thomas Edison held 1,093 U.S. patents, and hundreds more in other nations. His most famous work includes the incandescent light bulb, the phonograph, the alkaline storage battery, and a forerunner of the motion picture projector.