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.