A Custom Audience is a Meta Ads targeting option that lets advertisers reach users based on their own first-party data — including customer email lists, website visitors tracked via the Meta Pixel, app activity, or video viewers. It is one of the most powerful targeting tools on Meta because it targets people who have already demonstrated direct interest in a brand. Custom Audiences also serve as source lists for building Lookalike Audiences. As third-party cookies decline, Custom Audiences built from first-party data are becoming the foundation of effective Meta advertising strategy.