The definition of symbiosis is a commensal, parasitic, or mutualistic relationship between two organisms. Organisms form symbiotic relationships in order to make survival (housing, obtaining food, protection…) a lot easier. A commensal relationship is where the parasite organism benefits and the host has no effect. A parasitic relationship is where the parasite is benefitting and the host is being harmed in the process. A mutualistic relationship is where the both the parasite and the host are benefiting.