This post is typed verbatim from Keys to the Japanese Heart + Soul, an excerpt from Japan: An Illustrated Encyclopedia with additional input from Wikipedia.
A fundamental concept that has regulated Japanese society in various ways since ancient times. The Japanese traditionally attached overwhelming importance to one's "name," even to the point where it regulated one's actions.
With the rise of the warrior class in the twelfth century, the idea of "valuing one's name" (na o oshimu) came to occupy a central place in the psychological makeup of the Japanese. It is highly significant that the constant references to "name" (na) and "shame" (haji) in warrior tales are not limited to the honour of an individual but also encompass that of one's family and ancestors. Thus, shame to oneself is at the same time loss of honour to one's ancestors as well as descendants.
In the Edo period, the merchant class (chounin) appropriated the idea of honour from the warrior class and expressed it in such phrases as "bun ga tatanu" (I will lose my honour) or "otoku ga tatanu" (I will lose honour as a man).
In the Meiji period, when the state was presented as a patriarchal family, the historic lord-vassal relationship was held up as the model, and a renewed emphasis was given to the importance of honour. It was only with defeat in World War II that the Japanese began to reconsider the nature of honour in more personal terms.
Previously: Ojigi (Bowing)