Does an iTunes iOS device backup include everything on the device?

Does an iTunes iOS device backup include all of the application data on the device? I assume it doesn't include a second copy of your iTunes data as this is already on your Mac anyway. But I downloaded a lot of videos with the TED app on my device, while the size of the device's backup (*) seems comparatively small. Are these not included in the backup? If so, what other data might not be included? Is there a way to know what exactly is included or not (other than restoring from the backup)?

(*) = the folder ~/Library/Application Support/MobileSync/Backup

The backup contains:

• All your settings
• Application data except data marked as "cache" or not to sync.

Since iOS 5 there is a possibility for the developers to exclude some items from the backup.

There are ways to explore your backup, but I don't think this could give you definitive answer, wether your backup is complete or not. Developers should make sure that they don't exclude items from backup that cannot be recreated in some ways (download, rebuilding & etc). Some movie players offer to disable backups for their content, but this is configurable.

Because TED content can be downloaded at any time, probably the developers decided to not backup video content. Check the app for settings.