Review of ecological terms
Symbiosis: association of two different organisms living in close physical contact
Parasite: an organism that derives part or all of its food from another
Pathogen: an organism [or abiotic agent] that causes disease
Mutualism: association of two different organisms that is beneficial to both partners
Saprotrophic, saprobic: feeding on dead matter (saprophytic is also used, but implies that the organism is a plant which feeds on dead matter)