The SPDR S&P 500 ETF Trust is a very liquid exchange-traded fund which trades on the NYSE Arca under the symbol SPY. The ETF is designed to track the S&P 500 index by holding a portfolio comprising all 500 companies on the index. From Wikipedia
The Vanguard S&P 500 ETF overtakes the SPDR S&P 500 Trust after massive inflows, marking a significant shift in the ETF industry.
