This is the name of a fabulous horse in the mythology and folklore of Ireland. Aorbárr, whose name in Irish Gaelic means "Unique Supremacy", is also known by the name Enbhárr, which may be translated a "Froth" or "Foam". He is the steed of Manannán mac Lir and, as the name implies, was capable of dashing over any surface, whether mountain, marsh, or sea.
Devil Children Fire/Ice Book
Aonbharr can be found as random encounters in the Highest Peak and the Deep Hole.