What type of symbiotic relationship benefits one organism while harming the other?

In a parasitic relationship, one organism, the parasite, benefits at the expense of another organism, the host. The parasite derives nutrients and other benefits while harming the host, which may suffer from reduced health, reproductive ability, or even death as a consequence. This dynamic exemplifies a clear imbalance where the parasite's needs are fulfilled, often leading to detrimental effects on the host's survival or fitness.

Parasitism is distinct from mutualism, where both organisms benefit, and commensalism, where one organism benefits while the other is neither helped nor harmed. Cooperation involves mutually beneficial interactions, further highlighting the unique nature of parasitism, which is fundamentally characterized by the cost imposed on the host.