According to the study of statistics a random variable is one which can have any of a particular range of values, but does not have an equal probability of having each of those values. For example, the mark of a first year statistics student could be anything from 0-100% but it is most probable they will have a mark within two standard deviations of the median mark for the class.

The roll of a dice does not represent a random variable since there is an equal probability that it will land on any side. Statistics that are random variables are often expressed on a histogram.