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.
But before Thomas Alva Edison, people had no way of recording sound, much less capturing moving pictures. With 1,093 patents for inventions that range from light bulbs to cement, Edison was one of the world's most prolific tinkerers. Let's take a look at some of Edison's inventions that still inspire dreamers today: 1  The Phonograph (1877) -- Edison earned his nickname The Wizard of Menlo Park in November 1877 when he invented the world's first method of recording and playing back sound.