Define the segment
A churned or lapsed customer is someone who canceled a subscription, or whose last purchase/active-use signal has exceeded a threshold tuned to your typical repurchase or renewal cycle - a threshold that should come from your own historical repurchase-timing data, not an arbitrary default. This segment needs a clean transition rule out of "active customer" so it does not overlap with either the suppression or upsell segments.
Sync it
Sync frequency here can run slower than most other segments on this list - daily or weekly is usually sufficient, since the transition into "churned" itself is a slow-moving signal rather than a real-time event like a cart abandonment.
Why the creative differs
A win-back message has to acknowledge, implicitly or explicitly, that this person left once already - a generic acquisition ad ignores that context, and a suppression-style silence wastes a re-acquisition opportunity you already have first-party data to pursue at lower cost than cold prospecting. The offer structure that works for win-back (a distinct incentive, a "what's changed" message, a reactivation-specific CTA) is different from both new-customer acquisition and existing-customer upsell.
KPI framing
Measure reactivation rate and reactivation cost specifically against this segment, not blended into general retargeting metrics - and track how a reactivated customer's subsequent behavior compares to a newly acquired one, since win-back economics only make sense if the reactivated relationship holds past the initial reactivation event.
Illustrative, not a measured result: a subscription company builds a churned-customer segment with a 90-day lapse threshold and a "what's new since you left" win-back message, replacing a generic acquisition ad that had been reaching the same list by accident through an unsuppressed campaign. The expected effect of a dedicated win-back message over a generic one is a higher reactivation rate at a lower incentive cost than a blanket discount would require - illustrative of the mechanism, not a measured client result.