Mythology is a collection of myths, or sacred narratives, which cultures developed to explain how the world and how humankind came to exist and to explain how they are in their present form. Because myths are by definition sacred, and were considered true by the cultures who developed and related them, they often revolve around gods, supernatural beings, and heroic humans. Myth is closely linked to religion in ancient cultures, and sometimes the humans in the myths become gods or take on godlike qualities, as in the case of Amenhotep from Egyptian mythology.
While legend and folklore are closely related to myth, folklore and myth are not synonymous. Folktales are usually grouped into a different category from myth. The chief difference is that folktales, which are the stuff of folklore, are not considered true or sacred. Often myths are later reinterpreted as folktales, wherein the gods of myth become the fairies or ogres of folklore.
Greek mythology and Roman mythology are perhaps the best known of mythologies, and are extremely detailed and colorful. Roman mythology adapted many of the stories from Greek mythology, but changed the names of the deities (for example, Poseidon became Neptune, Aires became Mars). The lasting influences of Roman mythology and Norse mythology are evident in many modern words, such as the names of the planets and the names of the days of the week (Wednesday from Odin, Thursday from Thor--two of the gods of Norse mythology). Norse mythology also gives a detailed account of the gods and their doings, recounting the adventures of Odin, Loki the mischief maker, and including such elements as Ragnarok, the Norse mythological end of times.
Joseph Campbell, one of the foremost scholars on mythology, describes myths as having four basic functions. There are the Mystical Function, which serves to inspire awe in creation, the Cosmological Function, which explains why the universe is the way it is, the Sociological Function, which reiterates the value of social traditions, and the Pedagogical Function, which teaches humans how to live.
Folklore includes music, oral history, stories, popular beliefs and fairy tales and embodies the traditions of a culture. The study of folklore includes examining artifacts of folklore, the oral tradition of the stories told, and rituals and behaviors within the culture. Folklore serves to pass on knowledge and traditions of a culture, as well as to entertain and reinforce social values.