(1) A term Joseph M. Juran used to describe the Pareto principle, which he first defined in 1950. (The principle was used much earlier in economics and inventory control methods.) The principle suggests most effects come from relatively few causes; that is, 80% of the effects come from 20% of the possible causes. The 20% of the possible causes are referred to as the "vital few;" the remaining causes are referred to as the "useful many." When Juran first defined this principle, he referred to the remaining causes as the "trivial many," but realizing that no problems are trivial in quality assurance, he changed it to "useful many." Also see "eighty-twenty (80-20).
(2) These are the few (20%) independent variables, which contribute to maximum (80%) of the total variation. These are identified through Pareto Charts and Design of Experiments.