"Spoos" is a slang term used to refer to S&P 500 futures at the Chicago Mercantile Exchange, generally the front month. The S&P 500 is a market capitalization-weighted index of 500 leading publicly traded companies in the U.S. The index is considered to be a broad indicator of the performance of the U.S. stock market and is widely used as a benchmark for U.S. equity performance. The S&P 500 is considered a bellwether index, which means it is considered a good indicator of the overall direction of the market. The companies included in the index are selected by Standard & Poor's, a financial research and analysis firm, based on certain market capitalization and liquidity criteria. The index is calculated and maintained by S&P Dow Jones Indices.