Source : Webster's Revised Unabridged Dictionary (1913)

Parasitism \Par"a*si`tism\, n. [Cf. F. parasitisme.]
   1. The state or behavior of a parasite; the act of a
      parasite. ``Court parasitism.'' --Milton.

   2. (Bot. & Zo["o]l.)The state of being parasitic.

Source : WordNet®

parasitism
     n : the relation between two different kinds of organisms in
         which one receives benefits from the other by causing
         damage to it (usually not fatal damage)