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 Edisonâs Phonograph. Considered to be the first great Thomas Edison invention, and his life-long favorite, the phonograph would record the spoken voice and play it back.