Affinity is best described as the tendency or likelihood of a user to perform a certain action. In this instance, Quantcast views a particular site’s entire audience, and gauges how likely they are to visit another specific site. The number is a representation of this group’s tendency to visit that other site compared to the rest of the Internet.
For example:Site A has a 14.0x affinity to site B
This means that a visitor from Site A is 14 times more likely to also visit site B, in comparison to the average Internet user.