In the comments of his last post about comments you will see a discussion about what is and what is not a backup.
In short any kind of copy of your data is or can be a backup. It is however not a backup strategy. Your backup strategy depends on the how you value your data or even parts of your data and how paranoid you want to be.
If you are a sysadmin you want to be very paranoid about your data, all of it. Because you are in charge of data that is not yours, so you have no idea about the intrinsic value of each and every document.
If you are the head of you family and you have all the pictures of your children on their then that data is important and your strategy should be appropriate for that situation. You will need off-site copies and you will like on-site copies. You will also want multiple copies.
Do you need multiple copies of your OS-drive? No, but it can be very handy if you have an image available so you can restore it quickly when disaster strikes. But if your house burns down you will probably need to buy a new laptop anyway and then that image is pretty much worthless anyway.
So let's just say that the people in the comments where not completely wrong but we can not rely on "normal" users to know those difference, and it is always better to be safe then sorry.
Also keep this in mind: local backups are for fast recovery of small disasters, external backups are for slower recovery of bigger disasters.
So tell your friends and family to have as much copies as possible in different places. And they should write it down too. Because we all know how they remember their wifi password when we need it.
And a disaster never happens when you want it to happen.