law: Negotiable Instruments Act, 1881 
  5. "Bill of exchange" 
  A "bill of exchange" is an instrument in writing
  
  containing an unconditional order, signed by the maker, directing a certain
  
  person to pay a certain sum of money only to, or to the order of, a certain
  
  person or to the bearer of the instrument.
  A promise or order to pay is not "conditional" within
  
  the meaning of this section and section 4, by reason of the time for payment of
  
  the amount or any installment thereof being expressed to be on the lapse of a
  
  certain period after the occurrence of a specified event which, according to
  
  the ordinary expectation of mankind, is certain to happen, although the time of
  
  its happening may be uncertain.
  The sum payable may be "certain", within the meaning
  
  of this section and section 4, although it includes future interest or is
  
  payable at an indicated rate of exchange, or is according to the course of
  
  exchange, and although the instrument provides that, on default of payment of
  
  an installment, the balance unpaid shall become due. 
  
  The person to whom it is clear that the direction is given or that payment is
  
  to be made may be "certain person", within the meaning of this
  
  section and section 4, although he is misnamed or designated by description
  
  only.