\begin{definition}[Definition:Event]
Let $\EE$ be an experiment.
An '''event in $\EE$''' is an element of the event space $\Sigma$ of $\EE$.
'''Events''' are usually denoted $A$, $B$, $C$, and so on.
$U$ is often used to denote an '''event''' which is certain to occur.
Similarly, $V$ is often used to denote an '''event''' which is impossible to occur.
\end{definition}