Also known as Orestiad, it is a type of Nymph that lives in rivers, ravines, mountains, and valleys. Mountain Oreads were associated with Artemis, since she hunted in such places. They also tended to differ depending on the location.
"A type of nymph found in Greek Lore. Nymphs lived in and protect various places and general had different names accordingly. "Oread" was the name for the mountain nymphs, as opposed to the Napaea, who lived in valleys"
—Shin Megami Tensei IV Compendium Info
Oread is a pallette swap of Napaea, obtainable in the DLC quest "Experience of the Afterlife." A man in the only room on the map offers her fusion data in exchange for Light Grimoire x10.