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

unixism
 n.

    A piece of code or a coding technique that depends on the protected
    multi-tasking environment with relatively low process-spawn overhead that
    exists on virtual-memory Unix systems. Common unixisms include:
    gratuitous use of fork(2); the assumption that certain undocumented but
    well-known features of Unix libraries such as stdio(3) are supported
    elsewhere; reliance on obscure side-effects of system calls (use of sleep
    (2) with a 0 argument to clue the scheduler that you're willing to give up
    your time-slice, for example); the assumption that freshly allocated memory
    is zeroed; and the assumption that fragmentation problems won't arise from
    never free()ing memory. Compare vaxocentrism; see also New Jersey.


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

Unixism

    A piece of code or a coding
   technique that depends on the protected multitasking
   environment with relatively low process-spawn overhead that
   exists on virtual-memory Unix systems.

   Common Unixisms include: gratuitous use of "fork"; the
   assumption that certain undocumented but well-known features
   of Unix libraries such as "stdio" are supported elsewhere;
   reliance on obscure side-effects of system calls (use of
   "sleep" with a 0 argument to tell the scheduler that you're
   willing to give up your time-slice, for example); the
   assumption that freshly allocated memory is zeroed; and the
   assumption that fragmentation problems won't arise from
   never freeing memory.

   Compare vaxocentrism.  See also New Jersey.

   [Jargon File]

   (1995-02-27)