A parade of horribles is a parade in which people wear grotesque and usually comic costumes. It is a part of Fourth of July celebrations in many American communities, some of which have featured such a parade since the 1800s. This tradition probably has its roots in the death parades common in medieval Europe, in which someone would dress up as Death and lead a parade of "victims" across the countryside.
Adults and children dress up in monstrous costumes and lurch through the streets in a parade of horribles. The effect is often designed to be comic, with costumes which may reference ongoing social problems in an attempt to bring levity to serious situations. Spoofs of public figures, for example, can often be found leering at the audience, and elaborate parades may feature floats as well as marchers.
Parades of horribles are also seen in other regions of the world on major holidays. In all cases, the tradition is designed to give members of a community a creative outlet for expressing concerns with the direction their societies are taking, or simply a chance to have fun while dressing up in silly costumes. In a country with limited free speech, these events can sometimes be used as a vehicle for commentary on living conditions, since participants in the parade often have greater leeway than they would normally, especially because they are typically heavily disguised.
The term "parade of horribles" is also used rhetorically. Some people use the term literally, referring to a group of individuals who are considered responsible for a problem, as in "the parade of horribles at the agriculture department didn't regulate the industry as well as they should have." The term is also used to refer to a rhetorical device in which someone cites a list of theoretical outcomes of a decision in an attempt to dissuade someone from making that decision.