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

zigamorph
 /zig'@?morf/, n.

    1. Hex FF (11111111) when used as a delimiter or fence character. Usage:
    primarily at IBM shops.

    2. [proposed] n. The Unicode non-character U+FFFF (1111111111111111), a
    character code which is not assigned to any character, and so is usable as
    end-of-string. (Unicode is a 16-bit character code intended to cover all of
    the world's writing systems, including Latin, Greek, Cyrillic, Chinese,
    hiragana, katakana, Devanagari, Thai, Laotian and many other scripts ?
    support for elvish is planned for a future release).


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

zigamorph

   /zig'*-morf/ 1. Hex FF (11111111) when used as a delimiter
   or fence character.  Usage: primarily at IBM shops.

   2. [proposed] The Unicode non-character +UFFFF
   (1111111111111111), a character code which is not assigned to
   any character, and so is usable as end-of-string.

   [Jargon File]