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-Inventor (TV-14; 4:13) The inventor of the light bulb, phonograph, and motion picture, Thomas Edison was granted 400 patents from 1879 to 1886. Though he changed technology forever, not all of his inventions were successful.