The term 'Xeno' is a phrase used by the Imperium of Lenehen meaning any human who refuses induction into the Imperium, for example the other governments of earth in the early 21st century. However, in the late years of the 27th century, this term also grew to encompass hostile alien species, such as the Fra'al and Cadorians. The Ecclesiarchy state that such creatures pose a significant danger to mankind as well as standing in mankind's way of their manifest destiny to rule the Milky Way galaxy, and as such must be exterminated.