Clerics, druids, and shamen are referred to as priests, or "wis" casters. These casters are principally defensive in their spell line-up compared to their intelligence-based pure-caster counterparts, as their focus is more on keeping the group alive.
Clerics have the strongest direct-healing and heal-over-time (HoT) spell lines, and highest hit point buffs. Druids have strong direct-healing and regeneration spells. Shamen have comparitively weaker healing ability, but their buffs help to significantly mitigate damage by means of raising melee statistics (strength, dexterity, agility) to kill NPCs faster. Additionally, their stastic-reducing debuffs reduce an NPC's ability to kill through both slowing attacks and reducing armor class and resistence to spells.
Priests have sturider armor than intelligence-based DPS casters; they are not limited to wearing strictly cloth armor. Clerics can wear plate armor, druids can wear leather armor, and shamen can wear chain armor.
Priest classes utilize wisdom as their most important statistic. The base intelligence determines mana pool capacity for these casters. Hybrid classes based on these priest classes, the beastlord (shaman/monk), the paladin (cleric/warrior), and the ranger (druid/warrior), also utilize wisdom as a base statisic for their base mana pool and spell casting.