Short answers, pulled from the story.
One dominant theory translates the term as Odin's horse, linking it to Odin's self-sacrifice on a tree. Another scholar F. Detter proposed that the first syllable refers to terror rather than Odin creating a meaning of tree of terror or gallows. A fourth possibility from F. R. Schröder derives the name from words meaning yew pillar suggesting a structural support function.
The earliest written records of Yggdrasil appear in the 13th century within the Poetic Edda and Snorri Sturluson's Prose Edda. The poem Völuspá mentions the tree in its second stanza when a völva recalls nine worlds existing under a seed described as a glorious tree of good measure. Stanza 20 introduces three maidens named Urðr Verðandi and Skuld who incise slips of wood and choose lives for humanity beneath the tree.
One root reaches Hel while another reaches frost jötnar and the third extends over Niflheim where humans live. Beneath the first root of Yggdrasil lies the realm of Hel while the second root supports the domain of frost jötnar. The third root stretches into Niflheim a misty world where the spring Hvergelmir bubbles endlessly.
During the events of Ragnarök the ash Yggdrasil will shake violently so that nothing remains unafraid in heaven or on earth. Two survivors named Líf and Lífþrasir hide within Hoddmímis holt to repopulate humanity after the cataclysm ends. This survival mirrors the creation story where humans originated from tree trunks known as Askr and Embla.
A massive birch tree stood atop a burial mound beside a farm in western Norway until it was felled in 1874 during festivals when ale was poured over its roots. Warden trees were venerated in Germany and Scandinavia as late as the 19th century serving as guardians that brought luck to communities. These rituals confirm the position of the tree as a source of luck and protection for both gods and men.