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1.
FWIK = From What I Know.

Used when making a statement based on your knowledge, but *may* not be 100% correct.
John: Is Jenny going out with Clive?
Paul: FWIK yes. They've been seeing each other for 3 weeks now.
by Adsy360 December 10, 2009
 
2.
Short for Friends With Inside Knowledge. This is used to describe friends who are emotionally attracted to each other but resist any type of physical advancements either because they find each other ugly or just because they think they shouldn't.
Jenny and Johnny were rumored to be FWIK's because they always had Starbucks together.
by Zombie Hunter February 20, 2009