A reader model is the term used for the hypothetical average person who is the target audience for a product.
A reader model can be made from the average behaviour of many product users by datamining things like loyalty cards.
Based on data collected from datamining, an 'ordinary individual' (everyman) can be constructed (modeled) to develop the best strategy for selling to consumers.
In plain language a reader model is used by corporations to predict who will buy the better mousetrap.
The 'everyman' is used by commercial musicians, writers, and the movie industry trying to make money from a product that will appeal to a mass audience.