Answer
Health statuses describe resource operational state: Healthy (working as intended), Progressing (still coming up), Degraded (failed, e.g., crash-looping pods), Suspended (paused, like a suspended CronJob), Missing (not present), and Unknown. ArgoCD aggregates per-resource health into an overall Application health.
Real-world example A Deployment with crash-looping pods shows Degraded, turning the whole Application health red until fixed.