Symbiosis

The condition of two or more different species living together in close association. This association is usually relatively protracted and often dependent. In the past, symbiosis implied mu­tual benefit, but the term is now used in a broad, neutral sense. The three principal kinds of symbio­sis reflect whether the relationship is beneficial to both (mutualism), beneficial to one and harmful to the other (parasitism), or beneficial to one and in­different to the other (commensalism).