A host in parasitism is an organism that provides a suitable environment and resources for a parasitic organism to live and reproduce. The host typically suffers some degree of harm, as the parasite draws nutrients or energy at the host's expense. This relationship exemplifies a form of symbiosis where one party benefits while the other is negatively affected. Understanding host-parasite interactions is crucial in fields such as ecology, medicine, and agriculture, as it informs strategies for managing disease and pest control.