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Used to back up a statement that is strongly true.
Person A: Dude, the performance of Berlioz's "Symphonie Fantastique" was the best thing ever!!

Person B: For seriously!
by Sho Fo-Sho March 09, 2009
Often used to show excitment with underlining uncertainty.
Person 1: I had a car crash, but no one was hurt
Person 2: For seriously?!!
by textfile232 January 10, 2006