(1) In this Part" provident society" means, a person who, or a body of persons (whether corporate or unincorporate) which, not being an insurer registered for the time being under Part II of this Act, carries on the business of insuring the payment, on the happening of any of the contingencies mentioned in sub- section (2), of--
(a) an annuity of or equivalent to 2[ one hundred] rupees or less, payable for an uncertain period, or
(b) a gross sum of 3[ one thousand] rupees or less, whether paid or payable in a lump sum or in two or more instalments over a certain period,
exclusively in both cases (a) and (b) of any profit or bonus not being a guaranteed profit or bonus. Explanation.-- For the purposes of this sub- section, a period is" certain" if its duration is ascertainable in advance and" uncertain" if its duration is not so ascertainable.