Glossary

Terms used throughout the Argo CD codebase, derived from docs/core_concepts.md, pkg/apis/application/v1alpha1/, and the controller code under controller/.

Term	Definition	Where to look
Application	A Custom Resource that points at one or more sources (Git/Helm/OCI) and a destination (cluster + namespace). Argo CD reconciles the rendered manifests into the destination.	pkg/apis/application/v1alpha1/types.go
AppProject	A namespace-like grouping of Applications with allowed sources, destinations, and RBAC roles. Used for multi-tenancy.	pkg/apis/application/v1alpha1/app_project_types.go
ApplicationSet	A factory CRD that uses generators (Git, list, cluster, matrix, …) to produce Applications.	applicationset/, pkg/apis/application/v1alpha1/applicationset_types.go
Source	The desired state input. May be a Git repo (with directory/Helm/Kustomize/Plugin), a Helm chart in an OCI/HTTP registry, or an OCI image. Multiple sources can be combined.	Source/ApplicationSource in types.go
Destination	The target cluster and namespace. Identified by API server URL or by Argo CD's internal cluster name.	ApplicationDestination
Sync	Apply the rendered manifests to the destination cluster, invoking PreSync/Sync/PostSync hooks. Implemented in controller/sync.go and gitops-engine/.	controller/sync.go
Sync status	Synced, OutOfSync, or Unknown. Comparison logic lives in controller/state.go.	controller/state.go
Operation	A single sync (or rollback) attempt with a target revision and prune/dry-run options.	OperationState in types.go
Refresh	Trigger a fresh comparison between Git and live state. Soft refresh reuses cached manifests; hard refresh re-clones.	RefreshType constants in types.go
Health	Per-resource status determined by gitops-engine health checks (or custom Lua). Aggregated to an Application health status.	gitops-engine/pkg/health/, util/lua/
Hook	A Kubernetes resource annotated with argocd.argoproj.io/hook that runs at PreSync/Sync/PostSync/SyncFail.	controller/hook.go
Tool / Source type	The renderer used: Helm, Kustomize, Directory, Plugin (CMP).	reposerver/repository/repository.go
Config Management Plugin (CMP)	A user-supplied plugin that renders manifests. Runs as a sidecar and talks to the repo server over a gRPC socket.	cmpserver/, util/cmp/
Repo server	Stateless service that clones repos and renders manifests on demand. Caches results in Redis.	reposerver/, util/git/, util/helm/, util/kustomize/
Application controller	Watches Applications and drives reconciliation. Uses sharding to scale across replicas.	controller/appcontroller.go, controller/sharding/
Cluster	A registered destination Kubernetes cluster, persisted as a Secret with a known label.	util/db/cluster.go
Repository / Repo creds	A registered Git/Helm/OCI source with optional credentials, also stored as a labelled Secret.	util/db/repository*.go, util/db/repository_secrets.go
Project role / token	An RBAC role inside an AppProject, optionally with bearer JWT tokens.	cmd/argocd/commands/project_role.go
Manifest hydrator	Optional pipeline that renders manifests once and commits them back to a "hydrated" branch via the commit server.	controller/hydrator/, commitserver/, util/hydrator/
Notifications	Engine that listens for Application changes and sends messages to Slack/email/etc. via templates and triggers.	notification_controller/, util/notification/, notifications_catalog/
RBAC policy	Casbin-based permission model that complements Kubernetes RBAC. Stored in argocd-rbac-cm.	util/rbac/rbac.go
Settings	Cluster-wide Argo CD configuration kept in argocd-cm and argocd-secret. Loaded by util/settings/.	util/settings/settings.go
Sharding	Strategy for distributing application reconciliation across multiple controller replicas.	controller/sharding/
Webhook	Inbound git/registry webhook handler that triggers refreshes.	util/webhook/webhook.go
Tracking method	How Argo CD identifies resources it owns (label vs. annotation+label).	util/argo/resource_tracking.go

For binary-name terminology see Architecture. For the differences between sync, refresh, and operation, see the application controller deep dive in applications/application-controller.