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 Alva Edison entered into a new and the fullest phase of his career when, at age of forty, he moved his talents and tools from Menlo Park to his great new laboratory at West Orange, New Jersey, on November 24, 1887. One of his first undertakings was the development of his favorite creation, the phonograph.