A non-resident Indian (NRI) is an Indian citizen who has migrated to another country, a person of Indian origin who is born outside India, or a person of Indian origin who resides outside India. Other terms with 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 blood) who have taken the citizenship of other countries.

A Person of Indian Origin (PIO) is usually a person of Indian origin who is not a citizen of India. For the purposes of issuing a PIO Card, the Indian government considers anyone of Indian origins up to four generations removed, to be a PIO. [1]. Spouses of people entitled to a PIO card in their own right can also carry PIO cards. This latter category includes foreign spouses of Indian nationals, regardless of ethnic origin. PIO Cards exempt holders from many restrictions applying to foreign nationals, such as visa and work permit requirements, along with certain other economic limitations.

The NRI and PIO population across the world is estimated at over 30 million (not including Pakistan, Bangladeshi and Sri Lankan diasporas).

The Indian government recently introduced the "Overseas Citizenship of India (OCI)" scheme in order to allow a limited form of dual citizenship to Indians, NRIs and PIOs for the first time since independence in 1947. It is expected that the PIO Card scheme will be phased out in coming years in favour of OCI.

Source:  blogs.ibibo.com