A non-resident Indian (NRI) is an Indian citizen who has migrated to another country. Other terms with the same meaning are (somewhat self-deprecating in context) desis, overseas Indian and expatriate Indian. For tax and other official purpose the government of India considers any Indian national away from India for more than 180 days in a year an NRI. In common usage, this often includes Indian born individuals who have taken the citizenship of other countries.
A Person of Indian Origin (PIO) is literally, simply 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 .
There is a huge NRI and PIO population across the world, estimated at around 25 million.
Moving on outThe most significant historical emigration from India was that of the Roma. Around the 10th century A.D, Muslim invaders tore through what is modern-day Afghanistan, destroying ancient Hindu and Buddhist communities. The Hindu Kush is where thousands of Indians were wholesale slaughtered. The remnants of the Indian community left to Europe, where they were ridiculed and persecuted as the Gypsies, (based on an account of their origins lying in Egypt). They adopted local religions such as Christianity and Islam, but combined some of their Hindu practices with the new faiths. It is possible that the Gypsy Christian saint Black Sarah may have been a Christianization of the Hindu goddess Kali. They also speak a distinct Indo-Aryan language of their own, Romany. Another major emigration from the subcontinent was to South East Asia. It started as a military expedition by Hindu, and later Buddhist, kings of South India and resulted in the settlers' merging with the local society. The influence of Indian culture is still strongly felt in South East Asia, especially in places like Bali (in Indonesia). However, in such cases, it is not reasonable to apply the label 'PIO' to the descendants of emigrants from several centuries back, especially since intermixture is so great as to negate the value of such nomenclature in this context.
During the nineteenth century and until the end of the Raj, much of the migration that happened was of a forced nature - export of (thinly disguised) slave labor to other colonies under the indenture system. The major destinations, in chronological order, were Mauritius, British Guyana, the West Indies (Trinidad and Jamaica), Fiji and East Africa. There was also a small amount of free emigration of skilled laborers and professionals to some of these countries in the twentieth century. The event that triggered this diaspora was the Slavery Abolition Act passed by the British Parliament on August 1, 1834, which freed the slave labour force throughout the British colonies. This left many of the plantations devoid of adequate work force as the newly freed slaves left to take advantage of their newly found freedom. This resulted in an extreme shortage of labour throughout many of the British colonies which was resolved by massive importation of workers engaged under contracts of indentured servitude.
An unrelated system involved recruitment of workers for the tea plantations of the neighboring British colonies of Sri Lanka and Burma and the rubber plantations of British Malaya (now Malaysia and Singapore).
During the Partition of India, there was a great deal of migration between India and Pakistan, primarily of Muslims relocating to West Pakistan and Hindus and Sikhs relocating to India. A similar migration took place on the East side of India in the Bengal region between East Pakistan (since 1971 the nation of Bangladesh) and the Indian state of West Bengal. In total, about 7 million Muslims shifted to Pakistan, 10 million Hindus and Sikhs went to India, and anywhere from 500,000 to 1 million people died in riots and religious strife. Government policy, especially in lieu of India's reaching out to expatriates for investment (and extending, in some cases, offers of dual-citizenship), has refused to recognize Pakistanis and Bangladeshis as, officially, Persons of Indian Origin. This interesting situation is not, of course, a denial of recent history, but a result of the divisive nationalism that exists between India and Pakistan and, to a lesser extent, Bangladesh.
After independence in 1947, the pattern of emigration naturally changed. At first Indians sought better fortune mainly in the United Kingdom, but later North America, especially the USA (with 1.7 million Indians in total), became the favored destination after change in Indian emigration law that made this possible. Some displaced PIOs in Africa (especially under Idi Amin in Uganda) and the Caribbean also reached the UK. Smaller numbers of Indians have also emigrated to the English-speaking countries like Australia and New Zealand.
After the 1970s oil boom in the Middle East, a large number of Indians emigrated to the Gulf countries. However, this was on a contractual basis rather than permanent as in the other cases.