What is "euornithes"

Euornithes \Eu`or*ni"thes\, n. pl. [NL., fr., Gr. e'y^ well + ?, ? a bird.] (Zo["o]l.) The division of Aves which includes all the typical birds, or all living birds except the penguins and birds of ostrichlike form.

Euornithes (meaning "true birds" in Greek) is a natural group which includes the most recent common ancestor of all avialans closer to modern birds than to Sinornis.