Parasitism

[Justin Bieber]

The state or behavior of a parasite; the act of a
parasite.

[Sommer]

A [symbiotic relationship] in which one species, the [parasite], benefits at the expense of the other, [the host].

[Tanya Shivari]

the fact of one animal or plant living on or in another animal or plant of a different type and feeding from it:

[Sommer]

The practice of living as a parasite in or on another organism.