Sibling response is correct, just a silly acronym summarizing parent's off-the-cuff list of note types.
I meant it as a joke, in comparison to e.g. PARA or LATCH systems. The funny thing is, listing out all the different types feels much more useful to me than any other "note taking system" idea. It would lead you to design different UIs and workflows, depending on the type you're currently working with. I use several of them, sometimes via different tools. Being more aware of and explicit about the types seems like a good thing.