What is the $\frac{80}{20}$ rule?

$20$ percent' of the total demand for products comes from $80$ percent of the target market.

$80$ percent of a firm's profits is generated from $20$ percent of its product line.

$20$ percent of a firm's products are never marketed to $80$ percent of consumers.

$20$ percent of heavy users account for $80$ percent of the total demand.

$80$ percent of a firm's products are marketed to only $20$ percent of the population.