What do indices mean? It is the outcome of a set of titles’ weighted average. As it is regarded as an accurate reflection of the trend of a certain market, it helps investors to get a clear and quick sense of what the performance of a particular stock market is. Whether it is the whole bag or a portion of it. What do stock market indexes mean? The Dow Jones Industrial Average, which covers the 30 New York Stock Exchange businesses with the highest capitalisation, is one of the most important ones. The top 500 companies by market capitalization are instead included in the S&P 500. The primary business sector indices are the FTSE Italia All Share, FTSE MIB, FTSE Mid Cap, and others.