The rem command in config.sys is like telling a computer to put earmuffs on something it doesn't want to hear.
When you start up a computer, it looks at a bunch of files to figure out how to work. One of these files is called config.sys. This file has a lot of instructions for the computer to follow when it starts up.
Sometimes, there might be a line in the config.sys file that the computer doesn't need to use. But instead of deleting it, you can use the rem command.
The rem command is short for "remark". It makes the computer skip a line in the config.sys file, like putting earmuffs on it so it can't hear it.
So, using the rem command is like telling the computer "Hey, don't worry about this line right now. We'll come back to it later, but for now just ignore it."
It's a way to keep the config.sys file organized and easy to read, and also to make sure that the computer isn't using lines that it doesn't need to.