An Indian citizen who stays abroad for employment/carrying on business or vocation outside India or stays abroad under circumstances indicating an intention for an uncertain duration of stay abroad is a Non-Resident Indian (NRI). (Persons posted in U.N. organisations and officials deputed abroad by Central/State Governments and Public Sector undertakings on temporary assignments are also treated as non-temporary assignments are also treated as non-residents). Non-resident foreign citizens of Indian origin are treated on par with NRIs.
A Person of Indian Origin(PIO) means an individual (not being a citizen of Pakistan or Bangladesh or Sri Lanka or Afghanistan or China or Iran or Nepal or Bhutan) who:
an Indian Passport at any time, or
who or whose father or paternal grandfather was a citizen of India by virtue of the Constitution of India or the Citizenship Act, 1955
The Overseas Citizenship of India(OCI) is an immigration status permitting a foreign citizen of Indian origin to live and work and in the Republic of India indefinitely.