A PersistentVolumeClaim is a request for storage - it asks the Kubernetes Cluster for a particular type of storage which it can use as a Volume. After submitting a PersistentVolumeClaim, the Kubernetes Cluster will provision a PersistentVolume, which will be bound to your PersistentVolumeClaim (sometimes called a PVC).
Why are there both PersistentVolumes and PersistentVolumeClaims?
When a PersistentVolumeClaim is deleted by a user, it follows a defined policy regarding cleaning up the actual data on the PersistentVolume (which you can think of as the actual disk itself). By default, PersistentVolumes are not deleted, which reflects Kubernetes safety-first attitude and design.