A Long Tail is a logarithmic distribution of values which is common for quite a few use cases. Typically, a small number of cases supplies a large portion of data/values or other input, while a lot of cases supply only a small portion.
The Pareto (80/20) Rule exemplifies and relates the Long Tail concept to economic behavior by stating that in typical business scenarios, 4/5 of the value is created by 1/5 of the deals.
The Long Tail and Pareto Rule are graphically presented as x/y plots and/or histograms. The area under the curve or in the histogram columns allows for visual analysis of a situation.