Kuden (oral instruction) (口伝)
"Kuden" is a method of orally transmitting information. It is also called kuchizutae. "Kuden" also means the act or the matter itself of transmitting information. "Kosho," "densetsu" and "densho" are synonyms of "kuden."
The word "kuden" has extended its meaning from the above 1, to mean that a master of traditional performance art or martial art orally teaches his or her disciples, the esoteric knowledge or secret techniques unique to each school of the art. It also refers to the esoteric knowledge or secret techniques, passed on in this way. Important matters or secret matters of each schools are orally passed on, in order to protect such information from being known to outsiders more than necessary. Although "koketsu" and "koju [or kuju]" are the synonyms of "kuden" in this meaning, they are not so much used these days.
The word "kuden" has further extended its meaning from the above 2, to mean the book recorded the esoteric knowledge or secret techniques. Such a book is also called "kudensho" or "densho." In other words, it is a book of secrets of the art. By transcribing information to be handed down, preciseness of the information can be improved while the risk of information leak is increased. Some period novels and dramas depict incidents involving such books.