"Seeding" is the short term for adding mature media to your new filter from someone else's (or your own if you have another freshwater tank) long-time-running filter. When you move some filter media you are also moving the bacteria that live on that media and they are providing the "seed" that will grow into a mature colony if tended properly.
I assume KK was wondering whether you'd ever worked it out to get a 1/3 donation from your gf's tank (I assume this would be worth a night on the town to her, not to mention you buying her a fresh set of media from which to subset new media material for her filter.)
~~waterdrop~~