Average: What is typical, common, normal in a given group (collection, class, set) of things.
There are various kinds of average in statistics, like the mean and the mode, though it makes sense to remark these are normally defined in terms of one characteristic only, whereas what one calls "average" intuitively, especially when attributed to human beings and other things with many complex features, are those in the group considered who have no special striking features.
Also, as soon as one introduces some mathematical-like average, one problem one easily generates is that no one in the group considered may be average, for the kind of reason that the average adult human being on earth has one ball and one breast.
This also shows two other things about average so-and-so's: What is the average of the so-and-so's depends much on the so-and-so's; the characteristics considered; and the ways of measuring them. And averages are characteristics of groups or sets rather than individuals or elements of the group (etc.).