A volume refers to a Cinder volume. A volume is a persistent block storage device which is stored on a centralized storage array. A volume represents a logical area on a disk or a storage device.
Any data that is stored on a volume is persisted until it is erased from the volume.
A volume must be mounted within an Instance for the volume to be accessible within the guest operating system. A volume is used for storage of dynamic data such as a database, or website files. A volume can be created from a volume snapshot, another volume, an image, or as a blank volume.
Volumes can be bootable or non-bootable. A bootable volume can be used to boot an instance from the persistent data store. Volumes can be attached to instances for persistent block storage. Unless otherwise specified, the data on the volume persists even after the instance is destroyed.