SPDRs stand for Standard and Poor’s Depositary Receipts. Known as "Spiders," SPDRs are units of an ETF that holds shares of all the companies in the Standard & Poor’s 500 Composite Stock Price Index (S&P 500). SPDRs closely track the price performance and dividend yield of the S&P 500. There are also SPDRs that track the performance of other indexes.
Investors who purchase a SPDR own approximately one tenth of the value of the S&P 500 and receive pro rata quarterly dividends less expenses of the ETF. Unlike an index mutual fund that can only be bought and sold at the end of each trading day, SPDRs trade throughout the trading day.