Last Seen

Last seen is the timestamp of a user's most recent recorded interaction, and it anchors recency, dormancy and churn risk.

If first-seen says when a user started, last-seen says when they were last around — and this second one is vital for spotting churn. The definition of dormancy and churn effectively rides on this attribute: a user whose last-seen has fallen behind a threshold (30 days, say) is counted as dormant or churned. The main trap is choosing the threshold: for a daily-use app, 7 days absent means danger; for a product used once a month, that same 7 days is entirely normal. So last-seen alone is a raw number; its meaning only emerges when read against the natural usage rhythm of that particular product.