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2.
A Jancy is a "female best friend" of your current boyfriend. They will spend all of their time with him and will ultimately steal your boyfriend and possibly threaten your feminity as well.

A Jancy will either act super nice and normal around you or the exact opposite.

They are commonly found in rebound relationships. Though, your boyfriend may leave you for legit reasons the Jancy will always be your boyfriend's safety net which builds on her attraction factor over yours.
Kate: Damn girl! Your boyfriend moved on fast! Who's the new girl now?!
Diana: Ugh! Who cares what her name is! Jake wouldn't shut up about her when we were dating! Seriously, she's a total Jancy!

Tim: Hey! You wanna chill this weekend?
Jake: Nah, I'm chilling with my Jancy. We're going to the movies at 2!

Tim: In the morning? That's late. Watch out, bro. I don't know if your girl will like that.
Jake: Oh, she doesn't know.
by AprilxMayxJune October 15, 2009
 
1.
A beautiful girl with a great personality. One of the best people you'll ever meet. She is sexy, smart, funny, and caring. Everyone wants to be around her all the time due to her great features.
John- "Are you going to see Tiffany tonight?"
Connor- "No man, I'm going to see Jancy. She's perfect.
by Paigeybaby August 18, 2011
 
3.
crazy little malu girl who talks with a very high squeaky voice. refer to caker.
stop being a damn jancy!
by Shequanda Lewis May 17, 2008