Definition:Probability Measure/Definition 1

Definition
Let $\EE$ be an experiment. Let $\EE$ be defined as a measure space $\struct {\Omega, \Sigma, \Pr}$.

Then $\Pr$ is a measure on $\EE$ such that $\map \Pr \Omega = 1$.

Also see

 * Equivalence of Definitions of Probability Measure