What type of relationship involves one organism benefiting while harming the other?

The type of relationship where one organism benefits while harming the other is known as parasitism. In parasitism, the parasite derives benefits such as nutrients, shelter, or reproductive advantages from its host, which suffers in the process. This relationship typically results in harm to the host, which can manifest as disease, malnutrition, or other detrimental effects.

In contrast, commensalism involves one organism benefiting while the other is neither helped nor harmed, and mutualism describes a relationship where both organisms benefit from the interaction. Synergism refers to an interaction where two or more organisms work together to produce a combined effect greater than the sum of their individual effects, which is not specifically a parasitic relationship. Understanding these distinctions clarifies why parasitism is accurately defined by the scenario described in the question.