Nobi is the Korean word for a system of servitude in place between the 4th and 19th centuries. It should not be confused with the Japenese word sharing the same Romanization meaning growth or lengthening. Its status diminished greatly during the latter half of the Joseon Dynasty, and it was eventually abolished (along with other aspects of the sinbun class system) with the adoption of the Gabo Reforms (1894–1896). Nobi can refer to both the system itself and to the people in the system.
Like the slaves, serfs, and indentured servants better known in the Western world, nobi were considered property or chattel. They could be bought, sold, and given as gifts. Their owners were responsible for their care and well-being, and to a certain extent, legally responsible for their actions. In practice however, virtually no legal protection was accorded nobi.
Nobi could own property in many cases, and were allowed to marry and rear children. Acceptable marriage arrangements for nobi differed according to circumstance. Occasionally they could marry commoners, or in a few cases, could become concubines to their owners. More often, however, they could only marry other nobi. Children born from nobi marriages were sometimes made nobi, or commoners, or were even abandoned altogether -- as decided by the nobi's owner.
Nobi were often made to work as servants, such as in the households of members of the Yangban class, or as field laborers, or as public servants in the courts. They were often people being punished for the commission of a crime or the failure to pay a debt. However, becoming a nobi voluntarily was possible; this might be done to escape crushing poverty. Some were tattooed with a distinguishing mark to denote their status and to dissuade escape.
The term nobi, and its proper translation into English, has been a subject of debate among historians. Some Korean scholars argue that the designation nobi refers to a servant class system (compare with serf and indentured servant), whereas noye (distinct from nobi) is the designation for slavery. However, non-Korean historians usually consider nobi to be slavery. 
The motivations for abolishing the institution of nobi with the Gabo Reforms, along with the entire sinbun hierarchical class system, are sometimes questioned. Some claim that the reforms were due solely to the actions of pro-Japanese factions in the Korean government. However, another major impetus for the reforms was the occurrence of the Donghak Peasant Revolution, an anti-government, anti-Yangban uprising of the lower classes in Korean society.
See also 
- James B. Palais’s chapter 6 in Confucian Statecraft and Korean Institutions: Yu Kyŏngwŏn and the Late Chosŏn Dynasty (Seattle: University of Washington Press, 1996)
- Rhee, Rhee Young-hoon and Donghyu Yang “Korean Nobi in American Mirror: Yi Dynasty Coerced Labor in Comparison to Slavery in the Antebellum Southern United States”