Answer
ArgoCD is a declarative, Kubernetes-native GitOps continuous-delivery tool. It runs in the cluster, watches Git repositories holding Kubernetes manifests, compares the desired state in Git to the live state, and syncs the cluster to match. It reports sync and health status and can auto-heal drift.
Real-world example ArgoCD is installed in the cluster and pointed at a Git repo; from then on it keeps the cluster matching the repo.