Magic Resist, or MR, is a defensive attribute that affects a player's ability to resist magical attacks. Similar to Evasion for physical attacks, magical resistance will block a magical attack resulting in no damage. The higher the value, the more often spells are blocked. Most classes benefit from Magical Resist, particularly for PvP combat.
Sorcerers and Spiritmasters are restricted to Cloth Armor, which has an inherently high MR. Although any class can wear cloth, Templars and Gladiators will opt for the heavier armor for enhanced physical defense and will need to increase their magical defense by other means.
Magical Accuracy is the counter stat for Magic Resist.