But in the case of university classes, you are in fact buying them, it ain't free. So the shopping cart actually does make sense even if its a terrible use of another use cases' interface.

When you see that, it’s clear a system/framework/etc. is being used for something it was not designed for

In college, we had a two-week stretch at the beginning of a new semester when you could audition classes and add/drop them at will. This was called the "shopping period", so in my view, the shopping cart analogy on the registrar's web site doesn't sound too out of place here. Of course, the logic behind it would need to be different from an off-the-shelf e-commerce cart.

Eh, not necessarily. There might be a thought on the UX team that shopping cart is something anyone can relate to, so they use that as the metaphor.

Exactly. There are folders and a trash can on my computer desktop for the same reason.

Yes, but to me, a “shopping cart” implies a purchase. It’s what I use at a grocery store to put my food and stuff in. A “cart” would be better term IMO despite just being a shorter form of “shopping cart”. But idk.

But you signing up for classes is you buying something.

I used a class registration system that wasn't this and didn't mention a "shopping cart" metaphor anywhere, but the system was exactly the same. Why object to calling it a "shopping cart?