A commensal relationship in biology refers to a type of symbiotic interaction between two organisms where one benefits while the other remains unaffected. This relationship is different from mutualism, where both parties benefit, and parasitism, where one organism harms the other. An example is barnacles attaching to a whale; the barnacles gain mobility and access to nutrients in the water, while the whale experiences no significant impact from their presence. Understanding such relationships is crucial for studying ecosystems, as they reveal intricate connections and dependencies among species, contributing to biodiversity and ecological balance.