The same as we apply it to living beings: we are made of specialized cells each doing their job to keep the whole system working, some of them are made for reproduction. Maybe planetary reproduction starts when one of its products colonizes another one (like us, humans)?

I know that's a very far-fetching idea/concept but I like to think in this way.

Life is a human construct. The rest of the universe just exists. We only place value in water based reproduction because it's what we are.

Exo/planet colonization? Terraforming Mars, for example, will create a Mars that will (eventually) look like Earth.

It created us didn't it?

For extremely wide definition of "created", yes. But that definition is not very useful, since it implies pretty much no useful causal links, just the mere fact "here's a bunch of matter, and here we are located in this place on it". Yep, but so what?