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1.
The means by which a group of cohabitating women (such as a sorority house or college dorm) wirelessly synchronize their menstrual cycles such that by the end of a school year every woman in the house has her period simultaneously.
"Wow, I mean, like, its like totally a cruel coincidence that we all have our periods before the big mixer this weekend! I was looking forward to whoring it up!"

"I know right? But its no coincidence, our whole house is a Vagfi hotspot.
by DrRagnarok July 27, 2009
 
2.
A built-in feature of vaginas. Causes the vaginas of two women who spend a lot of time together to sync up and begin their periods at the same time.
Guy1: Well, my girlfriend started her period yesterday.
Guy2: No way, so did mine! They hang out a lot, right?
Guy1: Yeah, they must have vag-fi or something.
by Pterodactyl Lover October 06, 2010