The Jargon File (version 4.4.7, 29 Dec 2003):

middle-endian
 adj.

    Not big-endian or little-endian. Used of perverse byte orders such as
    3-4-1-2 or 2-1-4-3, occasionally found in the packed-decimal formats of
    minicomputer manufacturers who shall remain nameless. See NUXI problem.
    Non-US hackers use this term to describe the American mm/dd/yy style of
    writing dates (Europeans write little-endian dd/mm/yy, and Japanese use
    big-endian yy/mm/dd for Western dates).


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

middle-endian

    Neither big-endian nor little-endian.
   Used of perverse byte orders such as 3-4-1-2 or 2-1-4-3,
   occasionally found in the packed decimal formats of some
   minicomputer manufacturers.

   See -endian.

   [Jargon File]

   (1998-08-09)