Laerad is the Norse Tree of Life, most commonly known as Yggdrasil. In its branches there lives a goat - Heidrun - which supplies milk to immortalized heroes who live within the halls of Valhalla.
The tree is known by many names, as things are wont to be in Norse mythology. In addition to Laerad and Yggdrasil, it is known as the World Tree and Odin's Horse.
Laerad was created from the corpse of the giant Ymir (slain by Odin, Vili, and Ve). It supports the entirety of the Norse universe and all the Norse realms (e.g. Asgard, Midgard, Jotunheim etc.).
One myth has it that Laerad will be set afire (by the fire giant Surt) to destroy all things. But this destruction will only lead to the rebirth of the universe, and not the final winter.