(PIO) means a citizen of any country other than Bangladesh or Pakistan, if
(i) he at any time held Indian Passport; or
(ii) he or either of his parents or any of his grandparents was a citizen of India by virtue of the Constitution of India or the Citizenship Act, 1955 (57 of 1955); or
(iii) the person is a spouse of an Indian citizen or a person referred to in subclause (i) or (ii).
Reference: https://dipp.gov.in/sites/default/files/CFPC_2017_FINAL_RELEASED_28.8.17.pdf