V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

LUN
       Logical Unit Number (SCSI)


The Free On-line Dictionary of Computing (30 December 2018):

Logical Unit Number
LUN

    (LUN) A 3-bit identifier used on a SCSI bus to
   distinguish between up to eight devices (logical units) with
   the same SCSI ID.

   (1999-02-11)