What does the $\text{'}80-20\text{'}$ rule in market segmentation imply?

What does the $\text{'}80-20\text{'}$ rule in market segmentation imply?

$80\%$ of profits come from $20\%$ of customers.

$80\%$ of market segments are not profitable.

$80\%$ of products are sold to $20\%$ of the population.

$20\%$ of products account for $80\%$ of sales.

$20\%$ of customers account for $80\%$ of sales.