VOO (Vanguard 500 Index Fund ETF) is an ETF offered by the Vanguard Group, which tracks the S&P 500 Index.
VOO: Vanguard 500 Index Fund ETF
VTSAX: Vanguard Total Stock Market Index Fund Admiral Shares
VTSAX (Vanguard Total Stock Market Index Fund Admiral Shares) tracks the CRSP US Total Market Index.