There are some things that you know to be true, and others that you know to be false; yet, despite this extensive knowledge that you have, there remain many things whose truth or falsity is not known to you. We say that you are uncertain about them. You are uncertain, to varying degrees, about everything in the future; much of the past is hidden from you; and there is a lot of the present about which you do not have full information. Uncertainty is everywhere and you cannot escape from it.
Dennis Lindley, Understanding Uncertainty (2006)
Risk is an uncertain event
(Exposure to) the possibility of loss, injury, or other adverse or unwelcome circumstance; a chance or situation involving such a possibility.
Risk is an uncertain event or condition that, if it occurs, has an effect on at least one project objective. (This definition, using project terminology, is easily made universal by removing references to projects). The probability of something happening multiplied by the resulting cost or benefit if it does.
