Rick is talking about a computer bug, a programming error that causes the game to run incorrectly in some way. For example, a bug in a non-player character’s dialogue might make it impossible to hand in a particular quest. Not all bugs are detrimental to the game, however, and some can even be beneficial to players. For example, a bug might allow players to walk through a section of wall, thereby avoiding a particular monster or trap. Although these bugs are not part of the game and are not supposed to be there, players often consider it fair game to use them to their advantage until they are fixed or removed. Information about the existence of these bugs will often be passed on through word of mouth and in gaming forums, and will sometimes become the established method to complete a particular quest or challenge.