par·a·sit·ism 
(părə-sĭ-tĭz′əm, -sī-)
(părə-sĭ-tĭz′əm, -sī-)n.
1. A relationship between two organisms of different species in which one is a parasite and the other is a host.
2. The characteristic behavior or mode of existence of a parasite or parasitic population.
3. Parasitosis.