look up any word, like sparkle pony:
 
1.
A genre of fanfiction centered around a fictional romantic/sexual relationship between lesbian twin sisters, Tegan and Sara Quin of the band Tegan and Sara.
tsfan1: Do you think Tegan and Sara are really in love with each other?
tsfan2: I'm not sure, but quincest sure is fun to read about!
by ColyPoly July 26, 2010
 
2.
Sexual relations between two players on the same muggle quidditch team.
Yeah, everyone on our team is dating. Lots of quincest going on.
by Peter Porky April 06, 2014