There are many varieties of board games. Their representation of real-life situations can range from having no inherent theme, like checkers, to having a specific theme and narrative, like Cluedo. Rules can range from the very simple, like Tic-tac-toe, to those describing a game universe in great detail, like Dungeons & Dragons – although most of the latter are role-playing games where the board is secondary to the game, serving to help visualize the game scenario.