AoE is an abbreviation for "area of effect" and refers to skills that don't target specific marks, but instead effect a defined area.These tend to be powerful skills that deal a lot of damage but also take a long time to cast before they can be used.
Typically magic-using classes, like wizards, are the most likely to have AoE skills. Many AoE skills are very
"showy" with lots of animation effects used and if many of the skills are used in the same area they can cause lag for the players and strain on the game servers.
Retha Example: Vic's meteor skill, Heaven's Fury, in Second Age of Retha is an example of an AoE skill.