An RPG, or role-playing game, is a type of game in which players assume the roles of characters in a fictional setting and take responsibility for acting out these roles within a narrative, either through literal acting or through a process of structured gameplay. There are several varieties of RPGs, including tabletop RPGs, single-player role-playing video games, and massively multiplayer online role-playing games (MMORPGs). RPGs typically involve quests, which see the player challenged with different combat and exploration challenges, and are usually governed by a set of rules. Many RPGs allow the player to upgrade their characters skills and acquire new ones throughout the game. RPGs can be further categorized into subgenres, such as action RPGs, tactical RPGs, and Japanese RPGs. While there is no necessary and sufficient definition of an RPG, most gamers agree that RPGs have a focus on characters, dialog, and/or quest.