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Words you will hear

Terms that get used in documentation as though everyone already knows them.

Word	What it means
Apply	Making the change for real. The step after plan.
Declarative	You describe the end result and the tool works out the steps to get there.
Delete marker	What S3 adds when you delete a file in a versioned bucket without naming a version. The file looks gone and is still stored underneath.
Drop-in file	A small config file in a .d folder that the main config reads in. Lets a tool change a few settings without owning the whole file.
Drift	The gap between what is written down and what is actually running. Usually created by a hand edit during an incident.
Finalizer	A marker on a Kubernetes object that makes deletion wait until cleanup finishes. On an Argo CD Application it means deleting the app also deletes what it deployed.
Handler	An Ansible task that only runs when another task reports a change. Used for reloads and restarts.
Idempotent	Running it twice is safe. The second run notices everything is already correct and does nothing.
Immutable	Cannot be changed after it is written. Used here about storage that refuses deletes for a set period.
Inventory	Ansible's list of machines, grouped by what they do.
Least privilege	Giving an account exactly the permissions it needs for its job and nothing more.
Lock file	Terraform's .terraform.lock.hcl. Records the exact provider versions used, and belongs in Git.
Manifest	A YAML file describing something you want running on Kubernetes.
Module	A reusable folder of Terraform, called from somewhere else with different settings.
Plan	Terraform's preview. Shows what would change and changes nothing.
Playbook	Ansible's file of steps, written in YAML.
Provider	The plugin that lets Terraform talk to a particular cloud.
Reconcile	Compare what should be true against what is true, then close the gap. What Argo CD does on a loop.
Remote state	Terraform's record kept in shared, locked storage, so a team can work on the same thing without overwriting each other.
Role	In Ansible, a reusable bundle of tasks. In a cloud, a set of permissions something can assume. The same word, two unrelated meanings.
Rotation	Replacing a key or password on a schedule so an old copy stops being useful.
Source of truth	The one place that decides what is correct. For these tools it is the Git repository.
State file	Terraform's record of what it created. Holds secrets in plain text, so it needs protecting.
Sync	Making a cluster match the repository.
Tag	A label on a cloud resource. Used here to record who owns it and how sensitive it is.

Missing something? The three tool pages define each term where it first comes up, in context, which is usually easier to remember than a list.