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 is most well known for his invention of the light bulb. Contrary to popular belief, Edison did not invent the light bulb; it had been around for a number of years. The electric lights at the time, however, were unreliable, expensive, and short-lived.