1) In Norse mythology, the World Tree, known as Yggdrasil, is a massive ash tree that connects the nine realms of existence. It is considered the center of the cosmos and serves as a conduit between different realms, including Asgard (realm of the gods), Midgard (realm of humans), and Helheim (realm of the dead).

2) The fingerprints of koalas are so similar to humans that they have been mistaken at crime scenes.

3) The intensity of cyclones is often measured using the Saffir-Simpson Hurricane Wind Scale, which categorizes them based on their sustained wind speeds.

4) Democracy is a system of government in which power is vested in the people, who exercise it through elected representatives. It allows for political participation, freedom of speech, and protection of individual rights and liberties.