"Metagaming is a broad term usually used to define any strategy, action or method used in a game which transcends a prescribed ruleset, uses external factors to affect the game, or goes beyond the supposed limits or environment set by the game. Another definition refers to the game universe outside of the game itself.
In simple terms, using out-of-game information, or resources, to affect one's in-game decisions."
If you want to apply it to Freelancer, it's rather easy. For example, I write a story that my Liberty Navy character is addicted to Cardamine (which is an illegal act). If you use the information provided in my personal story in order to attempt getting me kicked out of the Faction (In-RP) that is metagaming. You have used information that your character in question has no way of knowing.