What is a custom audience in Meta ads?

Meta's Business Help Centre lists two groups of sources¹:

• Your own data. A customer list (email addresses or phone numbers you upload to match with Meta users), website visitors tracked via the Meta pixel, app activity, catalogue interactions and offline activity such as in-store purchases.
• Engagement on Meta. People who watched your videos, opened your lead forms, or interacted with your Facebook Page, Instagram account or shop.

One marketing agency's guide says Meta hashes the email addresses in an uploaded customer list automatically². "Hashed" means the details are turned into scrambled codes before matching, so the raw list is not what gets compared.

Two jobs. You can show ads to people who already know you, which is retargeting. You can also exclude them, so you do not pay to advertise to people who just bought. Meta even has an exclusion-only customer list audience for that second job¹.

A custom audience is also the starting point for a lookalike audience: a way to reach new people who resemble your existing customers. Meta says you can use a Custom Audience to create one¹.

It uses your own customer data, so consent and data rules apply. Which basis you rely on, and whether a list may be uploaded at all, your counsel decides.

It also depends on the quality of what you collect: first-party data, meaning data a brand gathers directly from its own interactions with customers, such as orders, accounts and email sign-ups.

Meta's automated campaigns, such as Advantage+ sales campaigns, manage audience, creative, budget and placement with machine learning. Check what audience inputs a campaign still uses.

For where audiences sit in the account, see Meta Ads Manager account structure. For choosing channels by margin, read paid media strategy for ecommerce.