Druids are the priests of Sylanna, Elemental Dragon of Earth and living embodiment of Nature. As such they are granted control over the magic of the elements, which they call upon in times of peril.
The Druids, compared to the human Freemages, are still closer to nature and the elements. This reflects in them being a bit more resilient - it's not uncommon to meet Druids wearing a spear instead of magic foci. They favor earth, water and prime magic and have mastered the art of channeling mana through mysticism, which enables them to reach the biggest mana capacity of all classes.