Symbiosis refers to a close, long-term relationship between two different organisms where both parties benefit from and rely on each other for survival. This type of interaction can occur in various forms such as mutualism (both species benefit), commensalism (one species benefits while the other is not affected), or parasitism (one species benefits at the expense of the other). Symbiosis can be found in many different ecosystems, including marine environments where organisms like corals and algae form a mutualistic relationship.