Missions: These are books that are official Adventures that you can run a character made for Shadowrun Missions at gaming stores and conventions. What you accomplish in the mission follows you through other missions, like the old D&D RPGA or Pathfinder's Adventure Paths (These will always be listed as Missions and list a Season they are a part of - SRM 09-01 Started from the Bottom is the first adventure of the 9th season. All the seasons have an interconnected storyline and are meant to play from the first book onward to scale difficulty with the players).
Adventures: 6th Edition are not really about single-shot Adventures anymore, old adventures like Dreamchipper, Mercurial, and Queen Euphoria don't really have counterparts in the new edition.
Campaigns: These usually involve a plot hook and include a bunch of adventure ideas around that hook. Characters that go through these adventures are for home-games only and do not gain any advancement in the Missions games. 30 Nights and Assassin's Night are Campaign books for 6th Edition. Universal Brotherhood, Harlequin, and Renraku Arcology Shutdown are examples of previous editions.
Plot Sourcebooks: These books are used to update the Shadowrun universe. They may include some adventure ideas, but are basically info-dumps for players and GM's about what's going on in the SR Universe. Book of the Lost, Collapsing Now, and The Keichibi Code are 6th Edition examples of Plot books. Previous edition examples include The Clutch of Dragons, Portfolio of a Dragon: Dunkelzahn's Secrets, Shadows of North America, and Bug City.