The meaning of include under section 158B to 158BG 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 Income Tax Appellate Tribunal tried to explain the meaning of include.
Meaning of include defined by court
The phrase “include” used in section 158B to 158BG of the Income Tax Act came up before hon’ble ITAT-Mumbai in Sunder Agencies vs. Dy. CIT  63 ITD 245 (MUM. – TRIB.) and it explained.
Meaning : The definition of ‘undisclosed income’ in section 158b(b), begins with the words ‘undisclosed income includes’. Sometimes, some definitions use both words ‘mean’ and ‘include’. There, it may be regarded that an exhaustive explanation of the things intended to be caught in the net of the section is specified.
But where the expression is merely ‘include’, it does not have a restrictive operation so as to confine the scope of the section only to those things specified in the words following. When the legislature wants to enlarge the natural meaning of a word or a phrase, it uses the word ‘includes’ and, in such a context, an inclusive definition means that over and above the natural meaning of the word, the specially provided meaning of the word will also have to be attributed for the purpose of interpretation of that particular statute or that particular chapter.
But the word ‘include’ is suspectible of another construction, which may become imperative, if the context of the act is sufficient to show that it was not merely employed for the purpose of adding to the natural significance of the words or expression defined. It may be equivalent to ‘mean’ and ‘include’ and in that case it may afford an exhaustive explanation of the meaning which, for the purposes of the act, must invariably be attached to these words or expressions.
Section 158B to 158G of Income Tax Act
158B. In this Chapter, unless the context otherwise requires,—
(a) “block period” means the period comprising previous years relevant to six assessment years preceding the previous year in which the search was conducted under section 132 or any requisition was made under section 132A and also includes the period up to the date of the commencement of such search or date of such requisition in the previous year in which the said search was conducted or requisition was made :
Provided that where the search is initiated or the requisition is made before the 1st day of June, 2001, the provisions of this clause shall have effect as if for the words “six assessment years”, the words “ten assessment years” had been substituted;
(b) “undisclosed income” includes any money, bullion, jewellery or other valuable article or thing or any income based on any entry in the books of account or other documents or transactions, where such money, bullion, jewellery, valuable article, thing, entry in the books of account or other document or transaction represents wholly or partly income or property which has not been or would not have been disclosed for the purposes of this Act, or any expense, deduction or allowance claimed under this Act which is found to be false.
In this article, you can get the guidance from high court on the meaning of include under section 158B to 158BG of the Income Tax Act.
Updated up to Finance Act 2021.