REM

Enables you to include comments in a batch file or in your 
CONFIG.SYS file. The REM command is also useful for disabling 
commands. (You can use a semicolon (;) instead of the REM 
command in your CONFIG.SYS file, but not in batch files.)

Note:
1. This command can lead a comment:

REM This is a line of comment.

2. This command is useful for disabling commands.
For example:
Original command:

SCANDISK /ALL /CUSTOM

After disabling using REM:

REM SCANDISK /ALL /CUSTOM

This is convenient when applied where you may want to recover 
the command in the future.

For more information, please refer to MS-DOS Help or Windows NT 
command line command help.