Neither the ram nor the ssd is on chip. The ram is on package, the ssd is on board.
On chip means literally on top of the silicon, like how AMD X3D cpus mount the SRAM chip. On modern Apple devices the ram is mounted on the organic package substrate. The difference is significant, and it's shitty that Apple outright lied about it.
I think that particular definition of "on chip" is entirely your invention. I've usually seen it broadly used for anything on-package, whether it's on-die or on a separate die within the same package.
"On chip" definitely does not have much if any history of referring specifically to stacked dies with TSVs, because that has been a very niche packaging technique until recently, and "on chip" is a much more broadly used term.