Source : Webster's Revised Unabridged Dictionary (1913)

Porosity \Po*ros"i*ty\, n. [Cf. F. porosit['e].]
   The quality or state of being porous; -- opposed to density.

Source : WordNet®

porosity
     n : the property of being porous; being able to absorb fluids
         [syn: {porousness}] [ant: {solidity}]