Complex sentence: Sell in May and go away is an investment strategy for stocks based on a theory (sometimes known as the Halloween indicator) that the period from November to April inclusive has significantly stronger growth on average than the other months.
Split into simpler sentences: Sell in May and go away is an investment strategy for stocks. It includes a theory (sometimes known as the Halloween indicator) that the period from November to April inclusive has significantly stronger growth on average than the other months.