In Greek mythology, oreads (from the Greek oros, “mountain”) are the nymphs of mountains and grottoes. Like other nymphs, they were minor female divinities who were not immortal but were extremely long-lived, and they were generally regarded as kindly toward people.
Greeks sorted nymphs by the part of nature each one belonged to: oreads lived in mountains and caves, naiads presided over springs, rivers, and lakes, Oceanids were sea nymphs, and Dryads or Hamadryads watched over forests and trees.
Source: Encyclopaedia Britannica, Nymph (Greek mythology)
Image: Marble votive relief for Hermes and the Nymphs from the Cave of Pan on Mount Parnes, Attica (c. 300 BC), photo by Gary Todd, CC0, via Wikimedia Commons.