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 Lightbulb Let there be Light! Historians agree that Thomas Edison was not the inventor of the electric light bulb, but he did produce the first commercially viable one. Earlier light bulbs were experimented with as far back as 1802; and there were 23 others who had invented light bulbs, some of whom were still working on them at the time of Edisonâs work.