The original Macintosh had an Applications folder. App is what I use to cut through tech speak for people at work because the shortcut is less daunting. They have apps on their phone. They must not be scary like Programs and Applications.

I don't think there's a clear definition of either. I'd say if it has no UI, it's a program. And if it has a UI, I don't know if it's a program or an app.

But also, you're right. Here's an article from 1994 describing Visicalc as a "Killer App" from the late 1970's, that prompted people to buy personal computers.