law: Transfer of Property Act, 1882
  21. Contingent interest
  Where, on a transfer of property, an interest therein is created
  
  in favor of a person to take effect only on the happening of a specified
  
  uncertain event, or if a specified uncertain event shall not happen, such
  
  person thereby acquires a contingent interest in the property. Such interest
  
  becomes a vested interest, in the former case, on the happening of the event,
  
  in the latter, when the happening of the event becomes impossible.
  Exception: Where, under a transfer of property, a person
  
  becomes entitled to an interest therein upon attaining a particular age, and
  
  the transferor also gives to him absolutely the income to arise from such
  
  interest before he reaches that age, or directs the income or so much thereof
  
  as may be necessary to be applied for his benefit, such interest is not
  
  contingent.