Behavioral targeting (BT) is an advertising methodology that shows ads to users based on the sites they visit and their actions on those sites. It works by taking into account a user's browsing history, purchases, and online behaviors to establish patterns and target ads to the right people, in the right place, at the right time with the right message. While it allows for more optimized campaigns and retargeting, concerns about behavioral marketing include the use of personal cookies and potential privacy issues.