1) A term of friendship used to address an individual or group of people that use Amateur Radio (Ham Radio) or hang out on Amateur Radio or an Amateur Radio repeater.
2) A term used to describe an overly conspicuous Amateur Radio operator or operators engaged in a qso or walking around at a ham radio swap meet.
3) Any individual that possesses the ultimate geek accessory, an Amateur Radio licence.
Yo, radio dudes, whats going on out here?
See that licence plate and that antenna? He's a radio dude!
Did you hear that radio dude talking about crossdressing last night on the zed zed machine? What an idiot!
He's not a radio dude, he's a fucking CB'er.