Video game genres are used to categorize video games based on their gameplay interaction rather than visual or narrative differences.[1] A video game genre is defined by a set of gameplay challenges. They are classified independent of their setting or game-world content, unlike other works of fiction such as films or books. For example, an action game is still an action game, regardless of whether it takes place in a fantasy world or outer space.[2] Within game studies there is a lack of consensus in reaching accepted formal definitions for game genres, some being more observed than others. Like any typical taxonomy, a video game genre requires certain constants. Most video games feature obstacles to overcome, so video game genres can be defined where obstacles are completed in substantially similar ways.[citation