Logical Unit Number
LUN is a SCSI protocol term that refers to a logically contiguous piece of storage. This usually corresponds to a volume in a storage array or an individual disk drive on a parallel SCSI bus. The storage volume identifier gets mapped to a LUN by the host operating system and they are usually different.
A volume on a storage controller can be assigned different LUN numbers on different hosts. A volume on a storage controller can be partitioned into multiple volumes, and thus, LUNs by storage virtualization software. The storage virtualization software can reside on hosts or network virtualization boxes.