The meaning of hindu used in section 2(31) of the Income Tax Act is not defined in the act itself. But we can take guidance from decisions by various high courts. Here is an excerpt of the court’s order in which the Hon’ble Supreme court tried to explain the meaning of hindu.
Meaning of hindu defined by court
The phrase ‘hindu’ used in section 2(31) of the Income Tax Act came up before Hon’ble Supreme court in CIT Vs. Smt. Champa Kumari Singhi  83 ITR 720 (SC) and it explained.
Meaning: The word ‘hindu’ preceding the words ‘undivided family’ signifies that the undivided family should be of those to whom hindu law applies.
Section 2(31) of Income Tax Act
2(31). “person” includes—
(i) an individual,
(ii) a Hindu undivided family,
(iii) a company,
(iv) a firm,
(v) an association of persons or a body of individuals, whether incorporated or not,
(vi) a local authority, and
(vii) every artificial juridical person, not falling within any of the preceding sub-clauses.
Explanation.—For the purposes of this clause, an association of persons or a body of individuals or a local authority or an artificial juridical person shall be deemed to be a person, whether or not such person or body or authority or juridical person was formed or established or incorporated with the object of deriving income, profits or gains;
In this article, you can get the guidance from supreme court on the meaning of Hindu under section 2(31) of the Income Tax Act.
Updated up to Finance Act 2021.