It is just a short form of "OK".
Kyle: Wanna hang out with the boys bro?John: K
It's just a short form of "Ok".
Kyle: Wanna go to the the arcade this Sunday?
Jay: K.
Literal Meaning |Noun|: A regular cap ð§¢.
Figurative Meaning |Adjective|: A lie or you can say: "That's cap! ð§¢".
Example for literal meaning:
Kay: I just bought a cap! ð§¢
Is it good?
Creed: Well, sort of.
Example for figurative meaning:
Kay: BRO I JUST HIT 100 THOUSAND SUBSCRIBERS ON YOUTUBE!!!!
Creed: WHAT!? THAT HAS TO CAP! ð§¢