(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.