A man over the age of 18 that lives in his mothers basement, playing Call of Duty and most likely has an Match.com account. They lack social skills needed to survive in the real world, and their mother threatens them to leave at least once a week. They are usually fans of monster energy drinks and they have their mom drop them Mcdonalds though the laundry shoot. They probably have a website selling mods for ps3 and make about $12 each month. Another thing that can make you a basement dweller is having a World of Warcraft account.
Did you read the biography about the guy who invented World of Warcraft? Yeah, he is a hardcore Basement Fairy.