Noun or Adjective & used as an acronym: short for: "Get In the Gang". a term used when someone's getting all nosy into your conversation, and you really didn't want them included in the first place.
See also: Gigging
"Gawd, Leslie is such a GIG all the time. Yeah, I know what you mean. She's always butting in to our private conversations," or "Stop being such a GIG Jenn, it's none of your business!" or, "Sorry, I'm just gigging in on your convo..."