Segments come in two kinds, and the difference matters for how you use them.
LIVE SEGMENTS
A live segment re-evaluates continuously against its definition. As consumers meet or stop meeting the conditions, they move in and out automatically. "First-time scanners (7d)" is a live segment — its membership rolls forward every day. Use live segments for ongoing flows like welcome journeys or lapsed-consumer win-backs.
STATIC SEGMENTS
A static segment is a frozen snapshot taken at a point in time. Membership does not change after capture. Use static segments when you need a stable list — for example everyone eligible for a specific draw, or a control group for an A/B test where membership must not drift.
RULE OF THUMB
If you want the segment to always reflect "who qualifies right now", make it live. If you need a list that will not move under you, make it static.