In general, when 1 organism feeds off another but does not normally kill it outright, the predatory organism is called the parasite and the prey, the host.
Further definition is needed to separate parasites from predators and herbivores .
Parasitism - a close association between 2 species in which 1 member of the relationship benefits and the other is actively harmed. For the parasite, the relationship is obligatory metabolic dependence on the host. Usually initiates a strong immunological response from the host. Macroparasites - live within the hosts, but release infective juvenile stages outside the host's body. Short lived response by host, persistent infections, and hosts are subject to continual reinfection.