<p><strong>Noun:</strong></p><ul><li>The branch of biology dealing with the relations and interactions between organisms and their environment, including other organisms.</li><li>The set of relationships existing between organisms and their environment.</li><li>The set of relationships existing between any complex system and its surroundings or environment.</li><li>The branch of sociology concerned with the spacing and interdependence of people and institutions.</li><li>Advocacy for the protection of natural resources from pollution or its effects; environmentalism.</li></ul>