You probably mean arcane explosion or AE in short. It's a basic magespell used to do area of effect dmg in a radius around the mage. It deals arcanedamage, has no casttime and no cooldown. In vanilla it used to have a 1.5 second casttime, wich could be lowered by 0.3 seconds per talentpoint (maximum of 5 to make it instant) in the talent "improved arcane explosion" in the arcane talenttree of mages.
Many mages used to pull large amounts of mobs together to spamm AE until they where dead to gain a maximum of xp per time, grinding through lvls. Only few skilled mages where able to do this sort of grinding, without a partner dedicated to heal the mage through.
If you have any further questions about this spell, google it <.<