Elder is a creature type generally reserved for especially ancient or powerful beings. Unlike Elves or Goblins, Elders don't share a unified mechanical identity and usually appear alongside another creature type such as Dragon or Giant.
Magic's original five Elder Dragons: Nicol Bolas, Arcades Sabboth, Chromium, Palladia-Mors, and Vaevictis Asmadi, are particularly important to the game's history, having supplied the "Elder Dragon" in Commander’s original Elder Dragon Highlander name.