Someone who doesn't have an account on any social networking sites such as Facebook, Flickr, LinkedIn, Twitter, MySpace, Habbo, Friendster, Orkut, Bebo, Last.fm or dogging.co.uk
These individuals typically like to think they are invisible, but usually aren't. They also utilise same said sites to stalk other people online.
Also spelt rumor (US spelling).
"Don't give out my mobile number, dude, I'm a just rumour."