A combination of "for" and "real." Means "totally", and in some cases can be used in place of "I know right". Can be spelled "frealz", "forreals", etc.
It's also a way to agree with someone.
Person 1: Dude, did see that girl? She was so hot.
Person 2: Freals.
Person 1: I can't believe she'd do that! What a bitch.
Person 2: Freals! She's a big fat whore too!