Close living associations are called symbiotic relationships.

Parasitism is an example of such a relationship

In this situation, the parasite feeds upon the tissues or fluids or another organism, but usually does not kill the organism it feeds upon, as this would destroy its food supply.

The organism the parasite feeds upon is called the host organism.

An example of this sort of relationship would be fleas on a dog or athlete's foot fungus on a human.

Types of Symbiosis
* parasitism: the parasite benefits at the expense of the host
* mutualism: both organisms benefit from the association
* commensalism: one organism is benefited and the other is unharmed