So you just bought this great game from the Android Market, and notice it says you have to download another 600 jiggawatts of files to run it. Don't be alarmed or surprised, if you haven't seen this yet, you will. But what is all that stuff, where does it go, and how do you get rid of it? I'm glad you asked!
What it is -- most times it's media files needed by the application itself. In our example (Dungeon Defenders First Wave), in addition to the 8MB app you download from the Android Market, you have to download another 645MB of things like movies, sounds, and in-game textures. Doing it this way solves two problems -- it keeps 658MB apps out of the Market, and keeps 658MB apps out of your app storage.
If all that data isn't installed with the app, where does it go then? It goes to your SD card or internal storage. It's up to the application developers exactly where on your SD card it goes, but a quick peek from your computer will easily find it. In our example, all that DLC (downloaded content) goes into a folder named DunDef. It sits there, just waiting for the time when the app needs any of it, not taking up valuable space for your installed apps.
This brings up two very important points -- you can't play the game without the SD card inserted and mounted, and when you uninstall the app there's a lot of stuff left behind. Both are easy to take care of. Don't try to play Dungeon Defenders without the right SD card in place or while you have the SD card mounted to your computer, and remember to delete the folder if you uninstall the game and have no intentions of ever reinstalling it. Deleting it is easy -- use a file manager or hook your phone up to your computer, find the right folder, and delete it. Just make sure you pick the right folder!