Define Triple point of water?

Triple point is that temperature, at which the substance is found in all three states i.e. solid, liquid and gas. Every substance has different triple point, because Triple point is just above the freezing point and each substance has different freezing and boiling point.

Water has a Melting point or Freezing Point (MP or FP) of C or 273K and Boiling point (BP) C or 373 K. Since the triple point is just above the MP or FP thus Triple Point of water is C or 273.16K.