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1 definition by B. Dub

 
1.
An acronym for Flat-ass calm. Used by sailors, fishermen and people who spend time on the water to describe a sea like glass.
"Going surfing today?"
"Nah man, it's F.A.C."

--or--

"Good day for fishing, it's F.A.C. out."
by B. Dub March 14, 2012