Shannon Entropy. In many circumstances, experimental measurements are associated with the accumulation of individual results which, ultimately, qualitatively and quantitatively characterized our experimental observations. The presence (or absence) of a particular result of an individual experimental measure is called an event. An event which can take one of several possible values is called a random variable. Analogously, a random event is an event that can either fail to happen, or happens, as a result of an experiment. An event is certain if it can not fail to happen and it is said to be impossible if it can never happen.