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

condition out
 vt.

    To prevent a section of code from being compiled by surrounding it with a
    conditional-compilation directive whose condition is always false. The 
    canonical examples of these directives are #if 0 (or #ifdef notdef, though
    some find the latter bletcherous) and #endif in C. Compare comment out.


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

condition out

    A programming technique that prevents a section of
   code from being executed by putting it in an if statement
   whose condition is always false.

   It is often easier to do this than to comment out the code
   because you don't need to modify the code itself (as you would if
   commenting out each line individually) or worry about nested
   comments within the code (as you would if putting nesting comment
   delimiters around it).

   For example, in Perl you could write:

    if (0) 
    ...code to be ignored...
    

   In a compiled language, the compiler could simply generate no
   code for the whole if statement.  Some compiled languages such as
   C provide compile-time directives that achieve the same effect,
   e.g.:

    #if 0
    ...code to be ignored...
    #endif

   (or "#ifdef notdef").

   [Jargon File]

   (2013-12-08)