Custom audience
A custom audience is a list of known users (emails, phone numbers, pixel events, or video viewers) used for retargeting or seeding lookalikes.
What does Custom audience actually mean?
Custom audiences are platform-side lists of known users built from data you own: customer email lists, phone numbers, app users, pixel-detected visitors, video viewers, Instagram engagers. Each platform has its own format (Meta Custom Audiences, Google Customer Match, TikTok Custom Audiences), but the concept is universal.
Custom audiences serve two main jobs. First, retargeting: serve ads to users who already know your brand. Second, lookalike seeding: feed your highest-quality custom audience into a lookalike algorithm to find more users like them.
The quality of a custom audience is bounded by recency and engagement. A list of users who visited in the past 7 days converts better than a list of users from 90 days ago. Most teams maintain rolling windows: 7-day visitors, 30-day video viewers, 180-day customers, etc.
Example
A SaaS company uploads 5,000 trial signup emails as a Meta Custom Audience, then builds a 2% lookalike from it to find more potential trial users.
When it matters
Custom audiences are the foundation of retargeting and the seed of lookalikes. Quality of the source list determines downstream campaign performance.
Related terms
First-party data
First-party data is information you collect directly from your customers: purchases, signups, behavior on your site. Privacy-safe and durable.
Lookalike audience
A lookalike audience targets new users who resemble an existing source list, typically your customers or your high-LTV cohort.
Retargeting
Retargeting serves ads to users who have already interacted with your brand: visited the site, watched a video, or added to cart.
Pixel
A pixel is a JavaScript snippet on your website that sends user behavior events (pageview, add-to-cart, purchase) back to ad platforms.
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