The SPDR ETF, commonly referred to as Spider, is a type of exchange-traded fund (ETF) that tracks the Standard & Poor's 500 (S&P 500) index. The fund is accessible to a broad range of investors, as the price of the fund is a fraction of the index it tracks, i.e. if the S&P 500 is trading at $3,000, SPDR will trade at $300. As such, it has become the cornerstone of many investor portfolios.

Spiders were initially launched in 1993 and were the first successful ETFs in the US. As of 2021, they are managed and marketed by State Street Global Advisors, a financial services firm. The fund performance closely tracks that of the S&P 500, however the fund does not include dividends.

Spiders are a great way for investors to invest in the S&P 500 without having to buy individual stocks. This can be particularly attractive for investors who do not have the time and resources to monitor the stocks in the index on an ongoing basis. As the ETF tracks the S&P 500, investors will benefit from diversification across the index and the management of the fund itself, so that the price changes more in line with the index and portfolio rebalancing is taken care of.

Moreover, unlike mutual funds, spiders represent a cost effective way of accessing the S&P 500. ETFs are typically much cheaper than mutual funds and investors don't have to deal with any front- or back-end loads. As with any other investment, investors should be aware that the fund may be subject to market risk, and its value will fluctuate over time.

All in all, the SPDR ETF has become very popular because of its low price and its ability to gain exposure to the S&P 500 quickly and efficiently. As such, it is often seen as an attractive option for those investors who want to leverage its attractive features to gain exposure to the S&P 500 with minimal effort and cost.