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2.
to be completely knowledgeable on a particular subject; the authority

"Jennifer Aniston is the 30 on ruining her own relationships."

"That guy is the 30 on not being cool... he has a mullet!!!"
by the30 March 28, 2009
 
1.
(noun) 1. A happenin' jivesville, dig?
2. Something you gotta get with, kid.
"This is the 30s, kid, get with da times."
by Gangardo September 29, 2006