Which term refers to the harmful effects caused when one organism benefits at the expense of another?

The term that describes the situation where one organism benefits at the expense of another is parasitism. In a parasitic relationship, a parasite lives on or inside a host organism, deriving nutrients and energy from it, often harming the host in the process. This is distinct from other types of relationships such as mutualism, where both organisms benefit, and commensalism, where one organism benefits while the other is neither helped nor harmed. Symbiosis is a broader term that encompasses both mutualism and parasitism, referring to any long-term interaction between different species, but in this specific context of harm to one party, parasitism is the most accurate term.