REM

Used for remarks in batch files, preventing the content of the remark from being executed.

An example:

REM A remark that does not get executed
echo Hello REM This remark gets displayed by echo
echo Hello & REM This remark gets ignored as wished
:: This sentence has been marked as a remark using double colon.

REM is typically placed at the beginning of a line. If placed behind a command, it does not work, unless preceded by an ampersand, as shown in the example above.

Double colon (::) is an alternative to REM. It can cause trouble when used in the middle of sequences in parentheses, like those used in FOR loops. The double colon seems to be just a trick, a label that starts with a colon.

Links:

• rem at ss64.com
• rem at Microsoft
• Which comment style should I use in batch files?, stackoverflow.com

$ rem /?
Records comments (remarks) in a batch file or CONFIG.SYS.

REM [comment]