Retargeting in social media marketing is the practice of showing follow-up ads or content to people who already interacted with a channel, video, website, or product page. On YouTube and Meta platforms, retargeting audiences are built from video viewers, page visitors, engagers, and past customers, then re-served with tailored creative designed to move them further down the funnel. Because retargeted audiences are already familiar with the brand, campaigns tend to convert at higher rates and lower cost per action than pure prospecting.