Species whose introduction and/or spread by human action outside their natural distribution threatens biological diversity, food security, and human health and well-being. āAlienā refers to the speciesā having been introduced outside its natural distribution (āexoticā, ānon-nativeā and ānon-indigenousā are synonyms for āalienā). āInvasiveā means ātending to expand into and modify ecosystems to which it has been introducedā. Thus, a species may be alien without being invasive, or, in the case of a species native to a region, it may increase and become invasive, without actually being an alien species.