Gutmann-Beckett method is a way to clean up data from a device, like a computer, so that it can't be recovered anymore.
You know how sometimes you colour really hard with a pencil and it leaves marks on the paper even if you try to erase them? Gutmann-Beckett method is like using a bunch of erasers really, really hard until those marks disappear forever!
When you delete a file on your computer, it's like the pencil marks - they're still there but you can't see them. But someone with special tools might still be able to find them.
Gutmann-Beckett method is like using special chemicals and tools to erase everything on your computer completely. It makes it almost impossible for anyone to find anything you previously deleted.
It's important to use Gutmann-Beckett method when you're getting rid of an old computer or giving it to someone else, so they can't find anything that was on it before.