An exchange traded fund, or ETF, is a financial instrument which can be traded like a stock but tracks the value of a stock index. The AMEX offers several exchange traded funds. The most popular of these are QQQ, which tracks the NASDAQ 100, and SPY, which tracks the S&P 500. The AMEX created these to compete with the futures which are traded on other exchanges.
Our alerts server treats these just like normal stocks. We track each exchange traded fund which meets our price and volume criteria.