Looking today at week-over-week shares outstanding changes among the universe of ETFs covered at ETF Channel, one standout is the ProShares UltraPro S&P 500 (Symbol: UPRO) where we have detected ...

The S&P 500 is one of the most widely followed stock indexes, and its performance is used as a benchmark for the stock market at large. Here's what it is, how it works, and why it's important.