The Dow Jones Industrial Average (DJINDICES: ^DJI) is probably the one stock market indicator that most people can name right away. Dating to 1885, it's the second-oldest active market index, after sibling Dow Jones Transportation Average, and it's the most widely covered.
Today, there are 30 stocks that make up the Dow Jones Industrial Average. The total has grown over time: Initially, the index had just 12 components, representing the major public industrial companies of the day. Today, the 30 companies in the index cover all of the major sectors of the U.S. stock market except for transportation and utilities. One thing to remember: Despite its name, the DJIA hasn't been limited to traditional "industrial" companies for many years.
All of the companies in the DJIA are considered major players in their respective industries. Most are household names.
Source: Fool.com