Define symbiosis.

Symbiosis refers to a close and often long-term biological interaction between different species, where at least one of the organisms involved derives a benefit. This definition encompasses various forms of symbiotic relationships, including mutualism (where both organisms benefit), commensalism (where one benefits and the other is neither helped nor harmed), and parasitism (where one benefits at the expense of the other). The key element of symbiosis is that it involves two different species and emphasizes the reciprocal nature of their interactions in terms of benefits and effects. Understanding symbiosis is important in ecology and biology because these interactions can significantly influence the populations, community structure, and evolution of the species involved.