Here we go:
A different game (not a Funcom game) there was a dungeon that looped back so that the entrance and the exit were close together with a wall between them. A player could enter the dungeon, a few steps into the dungeon entrance they could turn toward the wall and attack. The attack caused the character to access a tear in the wall mesh and cause the game to believe they were in the exit area. The game would declare the dungeon completed and reward the prize without the character having to go into the dungeon use resources, mana, heals, and the like, and fight the final boss. The game allows this to happen; however, it is a glitch and doing this is considered exploiting the game.
My friend was Beta testing a game that has not been released yet. He sold the wrong item to a vendor, realized his mistake and used the “undo” button to reverse the sale. He realized he received the item back and still kept the money that was given for the item. This practice could be repeated by a player (if it were not reported) until the player held a large sum of currency. The game does allow it, but it was a glitch as the money should have been returned to the vendor. A player, had this gone live, doing this would be cheating, exploiting a glitch.
There are many, many other ways to exploit glitches, but my point is it is cheating. Even though the game allows it.