Custom Audience

A custom audience is built from data you already have — a customer list, website visitors, or app users — and uploaded to a platform for targeting or exclusion.

Custom audiences are the seed material for lookalike audiences and the backbone of retargeting. Google's equivalent is called Customer Match; both require the platform to match your data (usually hashed emails or phone numbers) against its own logged-in user base, so match rates are never 100% — expect meaningful data loss between the list you upload and the audience size the platform reports.