The CBOE S&P 500 BuyWrite Index is a benchmark index designed to show the hypothetical performance of a portfolio that engages in a buy-write strategy using S&P 500 index call options. The term buy-write is used because the investor buys stocks and writes call options against the stock position. The writing of the call option provides extra income for an investor who is willing to forego some upside potential. The BXM Index is designed to show the hypothetical performance of a strategy in which an investor buys a portfolio of the S&P 500 stocks, and also sells covered call options on the S&P 500 Index. Wikipedia