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

comment out
 vt.

    To surround a section of code with comment delimiters or to prefix every
    line in the section with a comment marker; this prevents it from being
    compiled or interpreted. Often done when the code is redundant or obsolete,
    but is being left in the source to make the intent of the active code
    clearer; also when the code in that section is broken and you want to
    bypass it in order to debug some other part of the code. Compare condition
    out, usually the preferred technique in languages (such as C) that make
    it possible.


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

comment out
commented out

    To surround a section of code with comment
   delimiters or to prefix every line in the section with a
   comment marker.  This prevents it from being compiled or
   interpreted.  It is often done to temporarily disable the
   code, e.g. during debugging or when the code is redundant or
   obsolete, but is being left in the source to make the intent
   of the active code clearer.

   The word "comment" is sometimes replaced with whatever
   syntax is used to mark comments in the language in question,
   e.g. "hash out" (shell script, Perl), "REM out" (BASIC),
   etc.

   Compare condition out.

   [Jargon File]

   (1998-04-28)