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.