a species living outside its native distributional range which has arrived there by human activity, either deliberate or accidental

species that are at risk of extinction

Convention on International Trade in Endangered Species of Wild Fauna and Flora

The evolutionary process by which a single species splits into two or more distinct species.

Charles Darwin's "On the Origin of Species"

a species that is not native to a specific location and has a tendency to spread to a degree believed to cause damage to the environment, environment human economy or human health

Wikispecies; an online project run by the Wikimedia Foundation to catalog all known species