An index composed of the 100 largest, most actively traded U.S companies listed on the Nasdaq stock exchange. This index includes companies from a broad range of industries with the exception of those that operate in the financial industry, such as banks and investment companies. Taobiz explains Nasdaq 100 Index Individual investors are able to gain exposure to the Nasdaq 100 index by purchasing exchange-traded funds (ETFs) that are specifically designed to track its performance. The most popular of these ETFs is known as the QQQQ.