From Gamasutra.com : "I talk a lot about episodic games, and every time I do I encounter a wide range of opinions on what "episodic" actually means. I recently wrote an opinion piece that promulgated GameTap's perspective on what it takes to call a game episodic and it boils down to this:
1. Each episode stands alone but is part of a larger whole.
2. Each episode has a relatively short duration of play.
3. Episodes are delivered on a regular schedule over a defined, and relatively brief, period of time that makes up a season.