Abominatrix got it spot on. But i do also think that the definition of punk has changed since the sex pistols and continues to change. I wouldn't call the sex pistols punk rock by todays standards. Back then you wouldn't call Blink 182 punk rock. It has kept some of the same values but the attitude changes quite a lot. Rebelling against authority, standing up for what you believe in, just doing whatever the hell you want, complaing at being an adolescant and being broken by love etc are all things punk rock have covered