Armor in Astaria is what protects you from physical harm. There are ways around armor, yes, but the overwhelming majority of what damage you face in combat as you level your character up will be damage armor stops. Furthermore, some armor offers resistance to other damage types. As a page listing all possible armor would be very, very lengthy, here are some links to lists of specific armor types:
Specific armor pages
Direct links to all specific armor pages currently existing in the wiki.