Where in the Bible does it say you're not supposed to gossip?

And exactly how do you define gossip? Where do you draw the line between gossip and important information that ought to be told? If you have reason to suspect your neighbor is a serial killer—say, there's a smell of rotting meat coming from his house and you often see him digging holes in his back yard—are you not supposed to tell anyone because that would be gossip?

"Gossip" is one of the things "Dr." Laura Schlessinger used to harp on (I used to listen when I drove to work, maybe 15 years ago.) but she never defined it to my satisfaction.

There's a potential for a serious discussion here.