Secrets in aion are the things that few players know about, but are not actually against the games rules.
One of the biggest aion secrets used are ways to complete quests in the game. So maybe there is a special way to kill a boss via getting around his minions. Or a great way to get to him via a shortcut in a dungeon. These secrets will help you complete quests.
The next major type of secret has to be great farming and leveling spots. With these farming and leveling spots you can know where to make a ton of easy kinah in the game and the best places to kill mobs. These secrets most players keep only underground so only a few elite players know about them. At taultunleashed we have all these major secrets so you can easily level in the game.
For premium aion secrets be sure to check out the forums.