Burakumin (部落民, buraku community + min people), Eta (literally, "full of filth") or hisabetsu buraku (被差別部落) is a Japanese minority group as well as Ainu, residing in Hokkaido, Japan's most northern island. Less commonly they are called Mikaihou buraku (未開放部落, literally meaning unfreed buraku).
A Japanese word 部落 buraku literally means a small community where people share production and living, usually in farms. However, today the term most of time is a short-hand for certain kind of people, who are called hisabetsu buraku. It is important to note there is no concrete term to refer to the people due to the nature of Japanese language where absence of referring words implies non-existence of matters.
The eta were generally relegated to tasks surrounding death and the dead, such as the handling of dead bodies, butchering, tanning, leather working, etc. Due to their involvement with such occupations, taboo under both Buddhism and Shinto, the eta were considered to be ritually "unclean". They were housed in separate settlements and were generally avoided by the rest of Japanese society. When dealing with members of other castes, they were expected to display signs of subservience, such as removal of headwear.
They are descendants of premodern outcast hereditary occupational groups, such as butchers, leatherworkers, and certain entertainers. Discrimination against these occupational groups arose historically because of Buddhist prohibitions against killing and Shinto notions of pollution, as well as governmental attempts at social control, besides then the government's policy that seeks to impose the hierarchical structure to the Japan's society. They occupied the lowest level of the social hierarchy of feudal Japan.
Because they don't spread widely in Japan, the discrimination heavily varies according to the region.
During the Tokugawa period, such people were required to live in special buraku and, like the rest of the population, were bound by sumptuary laws based on the inheritance of social class. In a court case of 1859 described by author Shimazaki Toson, a Meiji magistrate declared, "An eta is worth 1/7 of an ordinary person."
In a try to modernize Japan, the Meiji government abolished most derogatory names applied to these discriminated communities in 1871, but the new laws had limited effect on the social discrimination faced by the former outcasts and their descendants. The laws, however, did eliminate the economic monopoly they had over certain occupations.
Prejudice against eta lingered into the modern era, and according to human rights workers is still a factor today.  It has been alleged that traditionalist families in Japan's certain regions still check the backgrounds of potential in-laws to prevent intermarriage with descendants of eta families.
See also: Dazaemon (弾左衛門), a ruler in Tokyo of buraku people, Buraku abolishment movement (部落開放運動)