Herewith presenting a FAQ on the above :

Who is a non-resident Indian? 

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. (Persons posted in UN organisations and officials deputed abroad by Central/state governments and public sector undertakings on temporary assignments are also treated as non-residents).

Do NRIs require permission of RBI to acquire an immovable propertyin India ?

No. An Indian citizen resident outside India does not require any permission to acquire any immovable property in India other than agriculteral/plantation property or a farm house. However the purchase consideration should be met either out of inward remittances in foreign exchange through normal banking channels or out of funds from NRE/FCNR accounts maintained with banks in India.

Who is a person of Indian Origin ?

For investments in immovable properties A foreign citizen (other than a citizen of Pakistan, Bangladesh, Afghanistan, China, Iran, Bhutan, Sri Lanka, or Nepal) is deemed to be of Indian origin if, (i) he held an Indian passport at any time, or (ii) he or his father or paternal grand-father was a citizen of India by virtue of the Constitution of India or the Citizenship Act, 1955 (57 of 1955).