Vaginal Flowback is the stuff that plops out the vagina between 5-120 minutes after it has been ejaculated in.
The female body essentially rejects some of the seminal fluid, because it's pointless if it's not viable to make a baby with.
Picture this, it's an hour after you've fucked, and you're standing in line for a coffee before work, you suddenly feel a little leakage from your intimate area. Now you can turn to the barista and say 'JUST GOT MY VAGINAL FLOWBACK!', with a little wink. You're welcome.