A scenario is a series of linked episodes or sessions in which some kind of story unfolds. In the early days of role-playing games, published scenarios in Dungeons & Dragons and some other traditional role-playing games were referred to as modules, a term from wargaming indicating a scenario that could be plugged into a published game. Scenarios are often called adventures, especially as role-playing games have an action-adventure bias.
Several scenarios compose a campaign.
Because players in a role-playing game are free to make meaningful choices that impact the direction of their group's story, a published scenario can't determine how a group who play the scenario will experience it, particularly the ending. As such, published scenarios tend to take one of the following approaches to design:
- Detail the scenes and situations that the player characters are expected to face in a strictly linear fashion, either relying on the group's goodwill to follow the plot or on railroading by the GM. This is generally considered poor design.
- Provide an overall trajectory for the scenario and enough setting information that multiple routes can lead to a similar climax. If choices are involved, they tend to lead to the same outcome (possibly by means of uncertainty game-mastering).
- Detail the start of a scenario, perhaps with opening scenes and an initial trajectory, but allow for multiple possible endings or leave the conclusion open-ended.
- Provide a setting, its non-player characters, and some story hooks, and trust the gaming group to use those to initiate their own story from that starting point.