Final answer:
The Dow Jones Industrial Average is the oldest and most widely followed index of stock market performance in the world, based on the stock prices of 30 large companies.
Step-by-step explanation:
The index based on the stock prices of 30 actively traded large companies is called the Dow Jones Industrial Average. It is the oldest and most widely followed index of stock market performance in the world. The index was started in 1896 and is composed of companies from diverse industries, chosen by analysts at Dow Jones and Company.