Until I heard episode 108 of the Sages’ discourse, I was under the impression that a “West Marches campaign” in RPGs was defined by the following characteristics:
West Marches was a game I ran for a little over two years. It was designed to be pretty much the diametric opposite of the normal weekly game:
There was no regular time: every session was scheduled by the players on the fly.
There was no regular party: each game had different players drawn from a pool of around 10-14 people.
There was no regular plot: The players decided where to go and what to do. It was a sandbox game in the sense that’s now used to describe video games like Grand Theft Auto, minus the missions. There was no mysterious old man sending them on quests. No overarching plot, just an overarching environment.
The eponymous Westmarches Campaign was indeed
set in a frontier region on the edge of civilization (the eponymous West Marches). There’s a convenient fortified town that marked the farthest outpost of civilization and law, but beyond that is sketchy wilderness. All the PCs are would-be adventurers based in this town. Adventuring is not a common or safe profession, so the player characters are the only ones interested in risking their lives in the wilderness in hopes of making a fortune (NPCs adventurers are few and far between). Between sorties into the wilds PCs rest up, trade info and plan their next foray in the cheery taproom of the Axe & Thistle.
The whole territory is (by necessity) very detailed. The landscape is broken up into a variety of regions (Frog Marshes, Cradle Wood, Pike Hollow, etc.) each with its own particular tone, ecology and hazards. There are dungeons, ruins, and caves all over the place, some big and many small. Some are known landmarks (everbody knows where the Sunken Fort is), some are rumored but their exact location is unknown (the Hall of Kings is said to be somewhere in Cradle Wood) and others are completely unknown and only discovered by exploring (search the spider-infested woods and you find the Spider Mound nest).
PCs get to explore anywhere they want, the only rule being that going back east is off-limits — there are no adventures in the civilized lands, just peaceful retirement.
But that is not the element of the eponym that turned into the point of the developing term of art in RPG discussions.