Transmedia - way of telling stories across multiple platforms.
Nowadays every series showed on TV or in cinema, have extensions (back stories of characters, different endings, prequels, sequels) on the other platforms.
The Walking Dead originated from comic books and moved into TV series, web-series, various games, which concentrate on different characters and events. The only element that really connects it all is the world the action is set in.
GI Joe and Transformers started as a series of action figures/toys and moved into cartoons, live action movies, games, comics and even more toys.
Transmedia is not something happening only in western world, but also visible in Japanese manga/anime, e.g. Sailor Moon series had it's beginning in Sailor V manga, that lead into Sailor Moon manga and anime (with extra filler season and extra characters), movies (animated and live action), games and fan fiction, not to mention various toys and cosplays.
Shingeki no Kyojin (Attack on Titan) - currently the most popular series by fandom, manga started in 2009 (on going), there are also 2 other series that are getting published in the same time, concentrating on different characters and events. First season of anime finished airing few weeks ago. There are few games scheduled to be released by 2014, same for OAV.
Final Fantasy universe is not only limited to RPG games, but also had characters appearing in movies and OAVs, plus other games like Dissidia and Kingdom Hearts.
Speaking of, Kingdom Hearts is a very good example of trasmedia, merging characters from Disney universe with jRPG characters from Final Fantasy and The World Ends With You into one coherent story (stories). Various games appeared on different consoles, showing little bits of story and contributing to the vast universe.
Oh..is Rachet and Clank really getting a full feature movie?
Above examples shows how important is to make almost every new story transmedia, allowing audience to be much more broader and creating additional buzz. After all people likes to find out extra information about their favorite character or world.