I liked this quote on indiewire.com from the filmmakers, Gregg Kavet and Andy Robin, behind the independent film "Live Free or Die" (no, not the Die Hard sequel). Read the whole interview here.
"What is your definition of 'independent film'?
It's a spectrum. The cheaper it is, the more indie. The longer it took to get it made, the more indie. The harder it is to fit the premise in a title or poster or 30-second commercial, the more indie. Extra bonus points if you hit up more than 20 friends and family for money and favors. Automatic disqualification for sequels."