n. 1. (Statistics) a measure or estimate of the degree of confidence one may have in the occurrence of an event, measured on a scale from 0 (impossibility) to 1 (certainty). It may be defined to be the proportion of favourable outcomes to the total number of possible outcomes if these are indifferent (mathematical probability), or the proportion observed in a sample (empirical probability), or the limit of this as the sample size tends to infinity (relative frequency); measures of subjective probability are also used.2. also called axiomatic probability. the formal study of random or chance events, usually in terms of probability measure, independent random variables, and their generalizations. This arises in part from the study of permutations and combinations, and its results are applied to the analysis of empirical data by the construction of statistical tests, and are further developed in game theory and information theory. Compare statistics. See also conditional probability, Bayes's theorem.3. another word for probability measure.