Facebook Custom Audiences

Facebook Custom Audiences is a targeting option within Facebook Ads that allows advertisers to reach existing customers or leads. Advertisers can upload their own customer data, such as email addresses or phone numbers, to create custom audiences. Facebook then matches this data with its users to create a targeted audience for advertising. This helps businesses re-engage past customers, reach warm leads, and improve the ROI of their advertising campaigns.

Website: https://www.facebook.com/business/help/465232426838772