* Parasitism: This is the most common term used when one organism (the parasite) lives in or on another organism (the host) and benefits by deriving nutrients at the host's expense. This often involves harm to the host, though not always.
* Commensalism: This describes a relationship where one organism benefits while the other is neither harmed nor helped. For example, barnacles living on whales.
* Mutualism: This describes a relationship where both organisms benefit. For example, bees pollinating flowers.
The best term to use depends on the specifics of the relationship. If the organism is benefiting at the expense of the other, then parasitism is the most accurate term.
