Which type of relationship benefits one organism while harming another?

The relationship described in the question, where one organism benefits while the other is harmed, is known as parasitism. In parasitic relationships, the parasite derives nutrients or some form of advantage from its host, ultimately leading to a detriment to the host organism. For example, tapeworms live in the intestines of their host, absorbing nutrients for their own benefit while causing nutritional deficiencies and other health problems for the host.

To further clarify the context of the other options: commensalism describes a relationship where one organism benefits and the other is neither helped nor harmed, exemplified by barnacles attaching to whales. Mutualism involves both organisms benefiting from the relationship, such as bees pollinating flowers. Symbiotic relationships can encompass both parasitism and mutualism but do not specifically indicate one organism benefiting at the other's expense. Thus, parasitism accurately captures the nature of the harmful relationship discussed in the question.