The theory of consumer choice under situations of risk and uncertainty belongs to the field of microeconomics. Risk and uncertainty are sometimes interchangeable terms but their meaning is easily misunderstood. Frank Knight in his “Risk, Uncertainty and Profit” 1921, treated this subject and posed a fundamental distinction between the two, formulating the definition that, ever since, became the most widely used.
In a situation that involves uncertainty the outcome is unknown and agents cannot (or will not) assign probabilities to each outcome. Sometimes it is said that uncertainty is an unknown-unknown, while risk is a known-unknown, since agents assign probabilities to each outcome.