I was about to say that confusing the first two makes perfect sense because it's been a long time since the Desktop has had any real purpose beyond displaying a background image. Then I realised that the kind of people we're talking about probably have a shortcut for every single application they've ever installed on their desktop and have no idea how to delete them.

It's been an equally long period since screensavers had any actual purpose, being replaced by power saving features and screens without burn-in.

They're still somewhat useful with OLEDs, although even there turning the screen off is sometimes better.

It doesn't help that different brands of OS used different terms for the same thing.

The screen saver mixup makes no sense though. That can only mean one thing.

I'm clear on the first set but will cop to not having thought much about which of those is which in the second set.

I've seen the ones on the second set meaning completely different things from one application or environment to another. Even switching the meaning between themselves.