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 and a lot of cases supply only small portion
The Pareto (80/20) Rule exemplifies relates the Long Tail concept to economic behavior by stating that in typical business scenarios 4/5 of the value are created by 1/5 of the deals.
The Long Tail and Pareto Rule are graphically presentable as x/y plots and/or histogramms. The are under the curve or in the histogramm columns allows for visual analysis of a situation.