Modern [Street dance]? such as Hip hop are not considered Folk Dances because they do not meet the above criteria. In retrospect, all folk dances today would once have fit the criteria for street dances at the time they were originally danced. Of course, in retrospect most of these dances were also once danced by the higher social classes, too; the entire notion of the "common folk" having separate dance forms from the upper classes is somewhat of a misnomer.
Some examples of families of folk dances would be: