Under the Additional Disclosures heading of the fund overview for the Fidelity Extended Market Index Fund it states:
This description is only intended to provide a brief overview of the mutual fund. Read the fund's prospectus for more detailed information about the fund.
The Dow Jones U.S. Completion Total Stock Market Index is an unmanaged index that represents all U.S. equity issues with readily available prices, excluding components of the S&P 500.
Returns prior to September 8, 2011 are those of the Premium Class and reflect the Premium Class' expense ratio. Had the Institutional Premium Class' expense ratio been reflected, total returns would have been higher.
See https://fundresearch.fidelity.com/mutual-funds/summary/315911743 for the full description.
What is meant by "excluding components of the S&P 500" in the second paragraph? What are the components it is referring to and how can I know which ones are excluded from this index?