What it means
Retargeting is the practice of running ads aimed specifically at people who have engaged with your business before: previous website visitors, people who started a checkout, people who messaged you on WhatsApp, past customers. The audience comes from your pixel data, custom audiences, or CRM lists.
Common retargeting pools: cart abandoners (showed clear purchase intent, often just need a nudge), website visitors who did not convert, past purchasers (for upsell or repeat-purchase campaigns), CTWA conversation starters who did not finish booking.
Why it matters
Retargeted users convert at 3 to 10 times the rate of cold audiences. They already know the brand, they have demonstrated interest, and they need less convincing. Per-conversion costs on retargeting are typically a fraction of acquisition costs.
The ceiling: retargeting can only reach people you have already touched. It scales with your top-of-funnel volume. Most ad accounts run a hybrid: most spend on acquisition (cold audiences), a smaller dedicated budget on retargeting where the ROAS is much higher.
Example
A property agency sees lots of CTWA leads who reply once and then go quiet. They build a custom audience of those people, exclude anyone who actually booked, and run a retargeting campaign with a different creative ('Still thinking about that 2-bedroom unit?'). Cost per booking on retargeting is one-fifth of cost per booking on the cold acquisition campaigns.