A LUN or Logical Unit Number is the address of a disk (in earlier versions) or a disk device in storage networks (current usage).
Usage
Initially, the term was used in SCSI as a method for addressing disks within a device with a single SCSI Target ID , such as a disk array. LUN does not mean a separate hard drive; rather, it defines a virtual partition in a RAID array. At the same time, the same virtual partition of the array can have different LUN values for different hosts to which this LUN is assigned. It is also possible for the same host to have the same LUNs belonging to different storage systems (different SCSI Target IDs).
Thus, the full address of the disk ( physical partition of the hard disk ) on the SCSI device consists of the SCSI Target ID (unique for the host and defined by the driver) and the LUN , unique within the SCSI device and assigned to it in the settings or automatically in order.
At the moment, as a rule, this term is used in storage networks.