Definition - What does Symbiosis mean?
Symbiosis involves the interaction between two different species that live in close association with one another, usually to the advantage of both species. It is, in most cases, a mutually beneficial relationship between these two different organisms. It is different from normal interaction between species in that these species live together. Many forms of symbiosis are beneficial to both, but there are forms of symbiosis that harm one or both organisms.
Safeopedia explains Symbiosis
Symbiotic relationships can be obligate or facultative. Obligate symbiosis is a relationship where two creatures must work together, or they cannot survive. Facultative symbiosis is when species live together by choice. There are four main types of symbiotic relationships: parasitism, mutualism, commensalism and competition. In parasitism one species benefits at the expense of the other. In mutualism both species benefit. In commensalism one species benefits while the other neither gains or loses anything. Competition involves two organisms competing for resources.