Technically, an American is someone from the Americas - i.e. North or South America. However, it is so commonly referring to people from the USA that we'll just ignore that point for now.
An American is someone who lives in the USA. Not all americans are overweight, ignorant pricks with an addiction to burgers and flag waving. Some of them are actually friendly, intelligent people!
Remember, kids: just because meet or hear one person from a certain place doesn't mean that everyone from there is like it. Oh, and did I mention that the actions of the US government don't ALWAYS speak unanimously for every last citizen of the USA? Just wanted to clear that up.
They do think some wierd things, though.. They call football soccer, American football football, aluminium aloominum, jam jelly and so on. But belittling them for differences like that would be a bit petty of me, wouldn't it?
While playing a game, I once met an American who was a mindless, stereotyping, bigoted, ignorant prick. But did that make me hate all Americans? Well, yes. But eventually I got over it. I would like to find that guy and cave his skull in, though..