A non-resident Indian (NRI) is a citizen of India who holds an Indian passport and has temporarily emigrated to another country for six months or more for employment, residence, education or any other purpose.
A. A person who has gone out of India or who stays outside India, in either case-
I). For or on taking up employment outside India,
II). For carrying on outside India a business or vocation outside India,
III). For any other purpose, in such circumstances as would indicate his intention to stay outside India for an uncertain period.
A person of Indian origin (PIO) is a person of Indian origin or ancestry who was or whose ancestors were born in India or nations with Indian ancestry but is not a citizen of India and is the citizen of another country. A PIO might have been a citizen of India and subsequently taken the citizenship of another country.
Other terms with vaguely the same meaning are overseas Indian and expatriate Indian. In common usage, this often includes Indian-born individuals (and also people of other nations with Indian ancestry) who have taken the citizenship of other countries.
A citizen of any country (other than a citizen of Bangladesh or Pakistan) is deemed to be a Person Of Indian Origin (PIO), if,
I).He, at any time, held an Indian passport, II). He or either of his parents or any of his grand parents was a citizen of India by virtue of the Constitution of India or Citizenship Act, 1955, III). A spouse (not being a citizen of Bangladesh or Pakistan or Sri Lanka) of an Indian citizen or of a person of Indian origin is also deemed to be PIO.
The Overseas Citizenship of India (OCI) Scheme was introduced by amending the Citizenship Act, 1955 in August 2005. The Scheme provides for registration as Overseas Citizen of India (OCI) of all Persons of Indian Origin (PIOs) who were citizens of India on 26th January, 1950 or there after or were eligible to become citizens of India on 26th January, 1950 except who is or had been a citizen of Pakistan, Bangladesh or such other country as the Central Government may, by notification in the Official Gazette, specify.