The concept of risk is central to investing and corporate finance, yet there is significant divergence among finance experts and academics on its definition and measurement. A commonly cited definition of risk is volatility or standard deviation, but the author prefers a definition that captures the duality of risk, including both danger and opportunity. The Chinese symbol for crisis or big risk is often cited as a representation of this duality, with one symbol representing danger and the other representing opportunity. When measuring risk, there are several choices to be made, including whether to focus on upside or downside outcomes, whether to use price-based or accounting-based measures, and whether to consider total or non-diversifiable risk. The author notes that the choice of risk measure will depend on whether the marginal investors are diversified or not, and what is believed about financial markets and accounting data. The sample includes 48,156 publicly traded firms, and the author examines accounting-based measures of risk, including earnings volatility and debt burden. The author also explores price-based measures of risk, including the range of prices and the frequency of loss-making. The results show significant variations in risk across companies and sectors, with utilities and financials generally being less risky than energy and technology firms. The author concludes that the choice of risk measure is critical, and that different measures can yield different conclusions about the riskiness of a company or sector. The analysis highlights the importance of considering multiple perspectives and measures when evaluating risk, and the need for a nuanced understanding of the complex and multifaceted nature of risk.