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 legendary inventor Thomas Edison was the father of landmark inventions, including the phonograph, the modern light bulb, the electrical grid, and motion pictures. Here's a look at a few of his greatest hits. The Phonograph Thomas Edisonâs first great invention was the tin foil phonograph. While working to improve the efficiency of a telegraph transmitter, he noticed that the tape of the machine gave off a noise that resembled spoken words when played at a high speed.