The Dow Jones Industrial Average (DJIA), also known as the Dow Jones, is a stock market index that measures the performance of 30 large, publicly traded companies listed on stock exchanges in the United States. The DJIA is one of the oldest and most widely recognized stock market indices in the world, and is often used as a benchmark for the overall performance of the US stock market.

The companies included in the DJIA are selected by the editors of The Wall Street Journal, based on various criteria such as market capitalization, financial performance, and industry representation. Some of the companies that are currently included in the DJIA are Apple, Microsoft, Johnson & Johnson, Coca-Cola, and Goldman Sachs.

The DJIA is calculated by adding up the stock prices of the 30 companies and dividing the sum by a divisor that is adjusted for stock splits, dividends, and other corporate actions. The resulting number is then multiplied by a constant to arrive at the index value.

Investors and analysts use the DJIA to track the overall performance of the US stock market, and to gain insights into the performance of specific companies and industries. However, it is important to note that the DJIA is just one of many stock market indices, and should not be used as the sole indicator of market performance.