I have seen the acronym "AEDU" (or perhaps ADEU) used on the community boards at wizards.com, but haven't stumbled on the definition, and a google search goes nowhere (I doubt they're suddenly saluting in Catalan). It seems to have something to do with wizards, but what does it mean?
It refers to the basic structure of the powers that balances the classes and keeps the approximate effectiveness of powers between classes equal. (i.e. a 5th level daily in any class is approximately on par with a 5th level daily in any other class.)
At-Will, Encounter, Daily, Utility
Old classes had all of their powers within those types, while new Essentials classes dabble in modifying Basic Attacks.