happenin

happening

1. noun Something that happens; an occurrence or event. Oh, you missed quite a few noteworthy happenings while you were out town.
2. adjective, slang Cool or trendy. We need to go there for my birthday—it's the most happening place in the city right now.

What's happening?

What's going on? How are you doing? What's new with you? "Happening" is often colloquially shortened to "happenin'" or "happ'nin'." A: "Hey, Jake, what's happ'nin'?" B: "Not much, Mike. How you been?" What's happening, everyone? You all have a good weekend?
Farlex Dictionary of Idioms.

What's happening?

 and What's happ?
Sl. Hello, what's new? Hey, dude! What's happening? What's happ? How's it goin'?
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

happening

1. mod. fashionable; trendy; positive. (Collegiate.) Wow, that’s happening!
2. n. an event. The concert was a real happening.
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • a little
  • muck-raking
  • sweet
  • sweeter
  • not anything to boast about
  • gonzo
  • preppie
  • preppy
  • bulletproof
  • SBD