Adventure – A series of interconnected scenarios to lead to some resolution.
Campaign – A series of adventures liked by recurring characters or other factors to tell a story.
Encounter – A single event or scene, where the player’s interact with or engage within a scenario.
Scenario – A series of encounters where the story progresses to a sort of conclusion.
Session – A single date with a gathering of players, typically running through several encounters.
Setting – A collection of rules and descriptions of a world (or worlds) that the players engage within.
Story Arc – a series of interconnected adventures within a campaign.
If you compare this to a television series, an encounter is a scene of the show. Several encounters are linked to make a scenario. The scenario is nothing more than the coordination of several related scenes, usually in sequence, but could be happening simultaneously with different characters, which could be called an act. All of the scenarios are tied together to form the adventure, which could be related to an episode of a show. Several adventures may be tied together for a larger story, which is the story arc, or one of many plots of a season. All this takes place in a campaign which is the area that the character’s engage in, and interact with the story on. All this takes place in the setting, which is the universe guidelines, which sets the ‘universe rules’ – such as the Rating, target demographics, how many seasons there are and the like.