Yggdrasill (Old Norse 'Yggr's horse' or 'horse of terror, gallows' or 'yew-pillar'?) is the name of the world-tree. The roots of this evergreen ash tree reach out on three sides over the whole world. Men live under one, the giants under another and Hel under the third. The squirrel Ratatoskr runs up and down the trunk, an eagle sits in the branches and the dragon Níðhǫggr and numerous snakes (Góinn, Móinn, Grafvitnir, Grábakr, Grafvǫlluðr, Ofnir and Svafnir) gnaw at its roots. Four stags graze in its branches: Dáinn, Dvalinn, Duneyrr and Duraþrór. Beneath it lie three wells: Urðarbrunnr, Mimisbrunnr and Hvergelmir (maybe they are just three different names for the same spring).
Other names for Yggdrasill are Læraðr and Mímameiðr.