a combination of the phrases "for real" and "seriously", "for serious" can express agreement when used as an exclamation, it can also be phrased as a question.
Example 1:
person A: "Hey, I got a new cell phone today"
person B: "For serious?"
Example 2:
person A: "That girl is such a ditz"
person B: "for serious!"
by Jon Pan September 10, 2005
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Grave in quality or manner, or being of such importance as to cause anxiety.
- like making sure that your space shuttle is safe to use to re-enter a your own planet's atmosphere... THAT is serious.
by Anonymous February 1, 2003
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Slang word used in the north of london
meaning some thing good.

or

some one that does not find what they do important.
Them creps are serious cuzz.

or

"Your not serious"-JME of meridian crew
by Voltige K-I-D June 11, 2004
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what all dads are when they come home from work
damn he's serious
by potatosfromearth123 May 15, 2017
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a mix of for real? and are you serious?

u can add LY to serious if needed~
ll: we have homework tonite
kk: "are u for serious?"
by Anonymous March 14, 2003
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looking nice....as in someone/something that would interest you.
Wow! Shorty is looking serious in those jeans.
by Adrianne March 24, 2004
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It's just like fo' real, but it sounds funnier and sometimes doesn't make sense to people the first time they hear it. Sure to make people laugh.
Bob: Did you know Britney Spears got fat?
Janet: For serious? She used to have such great abs.
Bob: For serious.
by Joseph Eckersen September 22, 2007
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