In Norse mythology, the Yggdrasil tree plays a vital role in the cosmos, serving as the world tree that connects the nine realms. It symbolizes the interconnectedness of all existence, acting as a bridge between the gods, humans, and other beings. Yggdrasil is depicted as an immense, sacred ash tree, with roots stretching into various realms, highlighting the concept of balance and the cycles of life, death, and rebirth within the universe.