Folklore

Folklore refers to the set of stories, beliefs and practices within a culture or similar group.

In Toaru Majutsu no Index, folklore is used as the basis for certain forms of Magic.

Principles
The folklore (or lore) of a culture consists of a combination of many things, including legends, music, beliefs, sayings, rituals, customs, fairy tales and more. These can be passed down through several ways, including artifacts and oral tradition.

There are often similarities between certain pieces of folklore between different cultures. These similarities can often be traced to a common origin, however there are some pieces which have an unknown origin, somewhere between the cultures it has spread through. These pieces of folklore are referred to as having 'fallen into the cracks'.

Folklore is often conflated with mythology (and vice versa). The two share certain similarities and differences, though the exact boundary between them isn't entirely clear.

Urban Legends are a form of modern day folklore.