The expected value of loss was used to define risk by Wald (1939) in what is now known as decision theory. In finance, volatility of return is often equated to risk. Equivalence between risk and variance of return was first identified in Markovitz's 'Portfolio Selection' (1952). In insurance, risk involves situations with unknown outcomes but known probability distributions. It allows 'risk' to be used equally for positive and negative outcomes. This definition comes from Knight's 'Risk, Uncertainty and Profit' (1921). This links 'risk' to 'uncertainty', which is a broader term than chance or probability. This definition comes from Willett's 'Economic Theory of Risk and Insurance' (1901). This definition comes from Johnson's 'Dictionary of the English Language' (1755), and has been widely paraphrased, including 'possibility of loss' or 'probability of unwanted events'. Modern equivalents refer to 'unwanted events' or 'something bad that might happen'. This definition comes from Blount's 'Glossographia' (1661) and was the main definition in the OED 1st (1914) and 2nd (1989) editions. The earliest use of the word 'risk' was as a synonym for the much older word ' hazard', meaning a potential source of harm.

Many other definitions of risk have been influential: ISO 31000:2018 'Risk management - Guidelines' uses the same definition with a simpler set of notes. Some restrict the term to negative impacts ('downside risks'), while others include positive impacts ('upside risks'). Its complexity reflects the difficulty of satisfying fields that use the term risk in different ways. This definition was developed by an international committee representing over 30 countries and is based on the input of several thousand subject matter experts. Note 5: Uncertainty is the state, even partial, of deficiency of information related to, understanding or knowledge of, an event, its consequence, or likelihood. Note 4: Risk is often expressed in terms of a combination of the consequences of an event (including changes in circumstances) and the associated likelihood of occurrence. Note 3: Risk is often characterized by reference to potential events and consequences or a combination of these. Note 2: Objectives can have different aspects (such as financial, health and safety, and environmental goals) and can apply at different levels (such as strategic, organization-wide, project, product and process). Note 1: An effect is a deviation from the expected – positive or negative. The International Organization for Standardization (ISO) Guide 73 provides basic vocabulary to develop common understanding on risk management concepts and terms across different applications. International Organization for Standardization The Cambridge Advanced Learner's Dictionary gives a simple summary, defining risk as 'the possibility of something bad happening'.

Unwelcome circumstance a chance or situation involving such a possibility. (Exposure to) the possibility of loss, injury, or other adverse or While including several other definitions, the OED 3rd edition defines risk as: The Oxford English Dictionary (OED) cites the earliest use of the word in English (in the spelling of risque from its French original, 'risque') as of 1621, and the spelling as risk from 1655. Definitions of risk Oxford English Dictionary The international standard for risk management, ISO 31000, provides principles and general guidelines on managing risks faced by organizations. This article provides links to more detailed articles on these areas. The understanding of risk, the methods of assessment and management, the descriptions of risk and even the definitions of risk differ in different practice areas ( business, economics, environment, finance, information technology, health, insurance, safety, security etc). The international standard definition of risk for common understanding in different applications is 'effect of uncertainty on objectives'. Many different definitions have been proposed. Risk involves uncertainty about the effects/implications of an activity with respect to something that humans value (such as health, well-being, wealth, property or the environment), often focusing on negative, undesirable consequences. In simple terms, risk is the possibility of something bad happening. Firefighters are exposed to risks of fire and building collapse during their work. For other uses, see Risk (disambiguation).

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