“This is from second grade, and we were learning about native Americans in class and–actually it might have been earlier, but, uh, some early elementary school grade, my teachers told me that native Americans made dream catchers. And so we spent one art class making dream catchers, because they told us that if we made them and hung them by our beds we wouldn’t have nightmares anymore. And so I made one and hung it over my bed. It did not work.”
This is a native American tradition, often taught in schools as representative of their beliefs in some way. It’s supposed to be protective, saving the person who has one and hangs it over their bed from having bad dreams. It is also partially belief oriented–my informant did not believe in its abilities, and thus it did not work for him. The dreamcatcher’s main body is a circle, in which are threaded strings in a generally intricate pattern. This web presumably catches the nightmares, keeping them from reaching the person who sleeps beneath it. It is also often decorated, sometimes with feathers hanging down towards the sleeping person.
It occurs fairly frequently in popular culture when one is referencing native Americans. Its protective ability was actually demonstrated (with a few tweaks) in a skit from the television show Saturday Night Live, in episode 13 of season 25. It was used to protect the protagonist against a curse put on him by a homeless man, as long as he hung it above his bed. His protection ended when his wife accidentally knocked it down and broke it.