interaction

Interaction refers to the mutual influence between two or more entities, where the actions or properties of one affect the behavior or state of another. Interactions can be direct or indirect, transient or enduring, and may vary in strength depending on context and mediating factors.

In social contexts, interactions include communication, cooperation, negotiation, and conflict, occurring in everyday conversations, institutions, and communities. In technology, interaction often refers to human-computer interaction, the study and design of the interfaces through which users engage with devices and software. Interaction design seeks to optimize usability, accessibility, and user experience.

In science, interactions are fundamental to explaining phenomena. Biological interactions include symbiotic relationships and predator–prey dynamics; ecological interactions shape communities. In chemistry and physics, forces and couplings describe interactions between particles and molecules, such as ionic bonds, van der Waals forces, and fundamental forces like gravity, electromagnetism, and the strong and weak nuclear forces.

In medicine and pharmacology, drug interactions describe how one substance affects another's efficacy or toxicity. In statistics and data analysis, interaction effects occur when the impact of one variable depends on the level of another variable. Networks, systems theory, and complexity science study how interactions give rise to emergent properties, such as collective behavior and systemic resilience. Understanding interaction across disciplines helps explain how parts of a system influence one another and contribute to overall dynamics.