Definition:Probability/Formal Definition

Probability

Let $\EE$ be an experiment.

Let $A \in \Sigma$ be an event in the event space $\Sigma$ of $\EE$.

Let $\Pr$ be the probability measure of $\EE$.

Then the probability of $A$ is the value $\map \Pr A$.

Also denoted as

Some sources give the probability of $A$ as $\map P A$

Popular Treatment

Amongst the non-mathematically-literate of the world's population, a common form of rhetorical emphasis (usually used when asserting a falsehood of a personal and delicate nature) is to state a greater-than-$100 \%$ probability of an event.

A typical example of this could be seen on the Maury Povich Show, as follows:

Euniquea: I am five hundred thousand percent certain that Twyvone is the father of mah bay-bee ...
Maury Povich: Twyvone ... you are naaht the father.