Flywheel integration is probably a better term. I.e. not vertically integrating for the supply of your current product, but in such a way that demand for both is increased.
Jeff Bezos talks about it a lot. So it makes sense it would come up in the context of similarities between SpaceX's and Amazon's strategies.
Same here. I'm guessing it's a term that's come up in a few popular posts here (especially considering Jeff Bezos left Amazon a few weeks ago and he talks about it a lot in his book and in general) and is not part of the vernacular of commenters here. Similar idea for other circles that you might have heard it in.