According to Forbes Investopedia: A consequence of an economic activity that is experienced by unrelated third parties.
Fossil-fuel companies, real-estate developers, and automakers in the U.S. have made profits for years from the auto-system of human transport. Many economists have hailed the "great success" of the "American way of life." But these profits have uncounted costs - externalities. The people of Ecuador are paying for the auto-system "miracle" with higher cancer rates, a consequence of an economic activity that is experienced by unrelated third parties. read more on CommonDreams or click here for a list of autosprawl externalities.