Either directly subscribing to shares and debentures on a repatriable or non- repatriable basis, or through portfolio investment scheme NRIs are allowed to invest in both shares and stock.
As per the Section 2(V) of Foreign Exchange Management Act 1999, NRI is a person
Who resides outside India or has taken up employment outside India; conducting business activities outside India staying outside India for an indefinite or uncertain time period has been in possession of his Indian passport (provided he is not a citizen of Pakistan or Bangladesh) either of his parents or grandparents were Indian citizen (as per the Indian Constitution/ Citizenship Act of 1955)