The S&P 500 is a market free float-weighted index of the prices of 500 large-cap common stocks actively traded in the United States. The stocks included in the S&P 500 are those of large publicly held companies that trade on either of the two largest American stock market companies; the NYSE Euronext and the NASDAQ OMX.
After the Dow Jones Industrial Average, the S&P 500 is the most widely followed index of large-cap American stocks. It is considered a bellwether for the American economy, and is included in the Index of Leading Indicators.
The index is the best known of the many indices owned . S&P 500 refers not only to the index, but also to the 500 companies that have their common stock included in the index. The ticker symbol for the S&P 500 index varies. Some examples of the symbol are ^GSPC[1], .INX[2], and $SPX[3]. The stocks included in the S&P 500 index are also part of the broader S&P 1500 and S&P Global 1200 stock market indices.
The “S&P 500” generally quoted is a price return index; there are also “total return” and “net total return” versions of the index. These versions differ in how dividends are accounted for. The price return version does not account for dividends; it only captures the changes in the prices of the index components. The total return version reflects the effects of dividend reinvestment. Finally, the net total return version reflects the effects of dividend reinvestment after the deduction of withholding tax.
Here is the link listed out the names of all the 500 companies under s&p 500
source : wikipedia: