What is the relationship characterized by one organism benefiting at the expense of another known as?

The relationship in which one organism benefits at the expense of another is known as parasitism. In this type of interaction, the parasite derives some benefit—such as food, habitat, or reproductive advantages—while causing harm to the host organism. This can lead to a decline in the host's health or even death in extreme cases.

Parasitism is distinct from other types of interactions such as mutualism, where both organisms benefit, and commensalism, in which one organism benefits and the other is neither helped nor harmed. Competition refers to the struggle between organisms for the same resources within an ecosystem. Therefore, parasitism is specifically characterized by this unbalanced benefit, making it crucial to understand in the study of ecological relationships.