What is folklore in literature, as a genre, its origin, and its themes?

The term "folklore" originally referred to the culture of peasants and to the transmission of stories and songs, often passed down orally, that commented on the culture of a group of people who were generally illiterate (see the source from GCSU below). The genre of folklore encompasses not just stories, but also music, fairy tales, origin stories, dance, and other reflections of a culture.
According to the source from Yale, below, Bruno Bettelheim analyzed the themes and purposes of fairy tales and believed that they were connected to the unconscious fears and dreams of children. Many folktales help children make sense of their fears and dreams and instill in them the idea that one's struggles can be overcome. An example is the tale of "Cinderella," which captures a child's sense that he or she struggles and is treated unfairly among one's siblings. Cinderella's victory over her ugly stepsisters allows the child hearing the fairytale to have the fantasy of succeeding above one's siblings and peers and having one's greatness recognized. Another theme, according to the source from Yale below, is the connection between people and the animal word, as some animals in folktales are evil while others are good. Animals in folktales are generally anthropomorphic (turned into humans) so that children can come to understand them and relate to them.
http://teachersinstitute.yale.edu/curriculum/units/1984/4/84.04.01.x.html

https://faculty.gcsu.edu/custom-website/mary-magoulick/history.htm