A "host species" refers to an organism that provides a habitat or resources for another organism, often a parasite or symbiont. The host species supports the life cycle of the other organism, which may rely on it for food, shelter, or reproduction. This relationship can be beneficial, neutral, or harmful, depending on the nature of the interaction. In ecological terms, host species play a crucial role in maintaining biodiversity and ecosystem balance. For example, plants can serve as host species for insects, while animals may host various microorganisms. Understanding these relationships helps scientists study ecosystems and the impacts of environmental changes.