A fraternity is a brotherhood or sisterhood (quite a few of what people call sororities are technically women's fraternities because of their consitution) of people who believe in a set of common principles. Fraternities range from the Freemasons to the college fraternities you hear so much about and that I will focus on. The first fraternity was Phi Beta Kappa, founded in 1776 at William & Mary college to promote the dicussion of intellectual discourse. They became the honor society they are today after their critics grew so loud that they unveiled their secrets and shamed their critics forever. There are many college fraternities nowadays, with many common shared factors: a focus on fraternal regard towards one another (think of an idealization of sibling relationships), strong Masonic elements in their secret rituals, and a focus on development of the individual.

There are no bad fraternities; just the occasional bad chapter. Just because the chapter of a given fraternity on your campus might be cool or a bunch of drunken louts doesn't mean that all members of that fraternity are. Ideally, all fraternities get along, but when in college, emotions often run high and sometimes fraternities tear down the Greek system on a campus beating each other up.

Finally, though it is slightly off-topic, note that hazing is not just against the law in many states, but is also against the rules of many fraternities' national organizations.