At American colleges there are "fraternities", wherin a bunch of guys (to put it roughly) get a well-funded group together for the purposes of creating a more social environment. (read: throwing parties). They also have the benefit of helping network people... get jobs for them after school, find tutoring or study groups. These "frats" are named with greek letters and the whole 'scene' is referred to as "greek or greek life" Multiple chapters of the same frats can exist around different schools.
The requirements for getting into many frats usually involve hazing and casting out some less desirable people. Because of this some look at frats as snobby, preppy, and a bunch of rich kids getting together to miss the point of college.
The female equivlent is a sorority.