Placeholder KEP-5541: Report Last Used Time on a PVC

content/en/docs/concepts/storage/persistent-volumes.md

@@ -937,6 +937,42 @@ there is no default causes PVCs without `storageClassName` created at that time
 to not have any default, but due to the retroactive default StorageClass
 assignment this way of changing defaults is safe.
 
+### Unused PVC tracking
+
+{{< feature-state feature_gate_name="PersistentVolumeClaimUnusedSinceTime" >}}
+
+When enabled, the PVC protection controller adds an `Unused`
+[condition](/docs/concepts/workloads/pods/pod-lifecycle/#pod-conditions) to each
+PersistentVolumeClaim to indicate whether it is currently referenced by any
+non-terminal Pod.
+
+The condition has two states:
+
+`Unused` with status `"True"` (reason `NoPodsUsingPVC`)
+: No non-terminal Pod references this PVC. The `lastTransitionTime` records when
+  the PVC became unused.
+
+`Unused` with status `"False"` (reason `PodUsingPVC`)
+: At least one non-terminal Pod currently references this PVC. The
+  `lastTransitionTime` records when the PVC started being used.
+
+A Pod is considered non-terminal if its phase is not `Succeeded` or `Failed`.
+This means that a Pending Pod (even one that has not yet been scheduled) counts
+as using the PVC.
+
+The `lastTransitionTime` of the `Unused` condition can be used by cluster
+administrators, monitoring tools, and external controllers to identify PVCs that
+have been unused for a long time. For example, to find all PVCs that have been
+unused for more than 30 days, you could query for PVCs where the `Unused`
+condition has `status: "True"` and `lastTransitionTime` is older than 30 days.
+
+{{< note >}}
+The unused duration indicated by this condition may be shorter than the actual
+unused time because of processing delays in the controller or because the
+feature was enabled after the PVC was already unused. The condition is not
+updated when a PVC has `deletionTimestamp` set (that is, PVCs that are being deleted).
+{{< /note >}}
+
 ## Claims As Volumes
 
 Pods access storage by using the claim as a volume. Claims must exist in the

content/en/docs/reference/command-line-tools-reference/feature-gates/PersistentVolumeClaimUnusedSinceTime.md

@@ -0,0 +1,16 @@
+---
+title: PersistentVolumeClaimUnusedSinceTime
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: alpha
+    defaultValue: false
+    fromVersion: "1.36"
+---
+When enabled, the PVC protection controller adds an `Unused` condition to
+PersistentVolumeClaims that tracks whether the PVC is currently referenced by
+any non-terminal Pod. The condition's `lastTransitionTime` records when the PVC
+last transitioned between being in use and being unused.