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

SCSI-2

    A version of the SCSI command
   specification.

   SCSI-2 shares the original SCSI's asynchronous and
   synchronous modes and adds a "Fast SCSI" mode (<10MB/s)
   and "Wide SCSI" (16 bit, <20MB/s or rarely 32 bit).

   Another major enhancement was the definition of command sets
   for different device classes.  SCSI-1 was rather minimalistic
   in this respect which led to various incompatibilities
   especially for devices other than hard-disks.  SCSI-2
   addresses that problem. allowing scanners, hard disk
   drives, CD-ROM drives, tapes and many other devices to be
   connected.

   Normal SCSI-2 equipment (not wide or differential) can be
   connected to a SCSI-1 bus and vice versa.

   (1995-04-19)