Variables play a central role in the area of descriptive statistics. In accordance with this meaning, they are also of special importance for probability theory. Here the random character of the observation adds to the simple assignment-rule. This leads to the concept of the random variable. Events can easily be described with random variables. The basic events then also lead to theoretical counterparts of empirical distributions, the probability densities and distribution functions. Furthermore, theoretical parameter of position/level and dispersion as well as context/connection are introduced as theoretical counterparts of arithmetic means and variance.