it is a combination of "idiot" and "dork" if u couldnt tell. someone who has brain smarts (and/or street smarts)but refrains on using them for entertaining purposes. this person can be a class clown, or could be just very slow-minded.
Jack: "i love computers these days. they are better than sliced bread!!"
Penny: "Jack, you are such an idiork, that 'better than sliced bread' joke is like, two years old! get a life!!"
Jack: whats an idiork Penny?"
Penny: "You are, Jack."