Definition:Random Variable

Informal Definition
A random variable is a number whose value is determined unambiguously by an experiment.

Definition 3
Alternatively (and meaning exactly the same thing), the above condition can be written as:

Also known as
The word variate is often encountered which means the same thing as random variable.

The image $\operatorname{Im} \left({X}\right)$ of $X$ is often denoted $\Omega_X$.