Have you ever been questing along when all of a sudden a frost mage comes around the corner on his mount, aggros a dozen mobs, freezes them in place, and then AOEs them all to death?
If so, you've witnessed AOE farming, one of the more unique tactics used by mages for leveling or grinding.
AOE farming has never really clicked with me (and with the buffs to quest XP in 2.3, using it to level seems counterintuitive), but there are many people who swear by it. You can even go on Wowwiki and find a list of good locations for AOE grinding by level, if you're looking for the perfect spot to farm.
On the other hand, maybe you'd really like some details on how to get started. If so, friendly boomkin (and sometime mage) Delos of Lazer Chicken has the goods on the best talent points, gear, and strategies in his guide to AOE farming as a mage.
A lot of great points are covered, including the slightly tricky detail of transitioning from gathering up mobs while mounted to dismounting and freezing them in place. Says Delos:
When I have them reasonably tight together, I run through the center of them once more and simultaneously jump (on my mount) and cast Frost Nova. This is an important step because it does three things. One, the mobs move tighter together because they are mindlessly moving inwards towards you. Two, you frost nova them in place when they are in this close bunching. Three, because you jump you make it so that you are out of rage of their melee, at least by a couple of yards and can begin your Blizzard immediately.If you're looking to try out AOE farming, I can't think of a better place to start than this post.