Frak is a profanity which refers to the act of sexual intercourse. It is often used to denote disdain or as an intensifier. It was first used (with the spelling "frack") in the Battlestar Galactica TV series.
It continues to be used throughout different versions of the franchise as an expletive.
Frak carries roughly the same meaning and emotional connotations as the American slang, "fuck ."
As with "fuck," frak can be almost all parts of a sentence simultaneously. This makes possible such gramatically unlikely combinations as, "Frak the frakking frakkers!"