The difference between AdRoll and Facebook advertising lies in their focus and reach. AdRoll specializes in retargeting, allowing businesses to show ads to users who have previously visited their website, across multiple platforms like websites, social media, and email. Facebook advertising, on the other hand, is focused primarily on ads within the Facebook ecosystem, targeting users based on their interests, demographics, and behaviors. While Facebook offers powerful audience targeting and a large user base, AdRoll provides a broader cross-platform approach, allowing businesses to reach users beyond Facebook. Both platforms can complement each other for a comprehensive advertising strategy.