The storage concepts present in OpenStack are described in OpenStack documentation

https://docs.openstack.org/arch-design/design-storage/design-storage-concepts.html

Ephemeral storage

if the Virtual Machine is created with the option

"Create New Volume" - "No" https://creodias.eu/-/vm-created-with-option-create-new-volume-no

the disks associated with VMs are ephemeral, meaning that they will disappear when a virtual machine is terminated.

Persistent storage

if the Virtual Machine is created with the option

"Create New Volume" - "Yes" https://creodias.eu/-/vm-creation-option-create-new-volume-yes

and

"Delete Volume on Instance Delete" - "No"

the disks associated with VMs are persistant, meaning that they do not disappear when a virtual machine is terminated.