How Google infers interest and demographic categories
As users browse Google sites likes YouTube and our partner websites, Google stores an advertising cookie in a user's browser to understand the types of content that the user is viewing. This information is used to show ads that might appeal to your users based on their inferred interests and demographics.
For example, if a user browses many sports-related websites displaying AdSense ads or watches sports-related videos on YouTube, Google may associate a sports interest with their cookie or Google Account and show the user more sports-related ads. Similarly, if the sites that a user visits have a majority of female visitors, we may associate the user’s cookie or Google Account with the "female" demographic category. We may also use demographics from Google Accounts.
In some cases, Google may charge a service fee for personalized ads. In these cases, the advertiser’s maximum bid is reduced before the auction and the fee is added to the closing auction price.
Users can learn how Google uses their information and demographics and can opt out of Ads Personalization within Ads Settings.