What are Custom Affinity Audience Reports
These are cookies that track user behavior which allow the website owner to view what certain people view on their site. This is beneficial to the website owner because they can send personalized advertisements based on people website interactions.
Demographics, Interests and Geography
Audience Reports are a way to keep track of your users traits and behaviors while visiting your website. The Reports keep track of cookies of users like what sites they visit, where they do online shopping, how long they are on that site and more. The demographics are the characteristics of the user such as age, gender and language which help you give targeted advertisements based on the users characteristics. The audience reports help retain what the users interests are based on recent purchases, website views and and where they shop. This helps the the company send personalized ads for products that that person might be interested in purchasing based on past website interactions. Lastly, the geography will let you personalize the ads based on what language people speak. The audience reports will show you where people are from that are viewing your website which gives you an opportunity to make new ads in those languages.
Below is a link that goes into more details about costume affinity audience reports and how to use them.