Frost is one of the Mage's talent trees that focuses on keeping the mage's aggressors at a distance and providing the mage with excellent survivability; Mages who mainly invest into this tree are referred to as frost mages. Frost is often referred to as the spec of choice for leveling, giving the mage an edge over other spec's and even classes in the form of AOE grinding, which often nets bigger experience gains than solo questing. By utilizing key talents such as Permafrost, Improved Frost Nova and Improved Blizzard, a talented frost mage can round up and AOE down as many as 9 to 10 mobs at a time. While a frost mage's damage is respectable, it won't match that of a fire mage or arcane mage. Also frost is especially useful in kiting, allowing the frost mage to solo many difficult mobs.
In PvP, a frost mage can be frustrating to fight against considering their ability to use a well timed Ice Block to escape from a particularly heavy hit or to erase any debuffs they currently have. Also thanks to talents like Ice Barrier that can absorb a lot more punishment before waving the white flag.