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.
The American inventor Thomas Edison held hundreds of patents, mostly for electrical devices and electric light and power. Although the phonograph and the electric light bulb are best known, perhaps his greatest invention was organized research.