The following is from this Apple document: iCloud: Backup and restore overview.
iCloud automatically backs up the most important data on your device using iOS 5 or later. Once you have enabled Backup on your iPhone, iPad, or iPod touch .....
What is backed up
You get unlimited free storage for:
- Purchased music, movies, TV shows, apps, and books
- Notes: Backup of purchased music is not available in all countries. Backups of purchased movies and TV shows are U.S. only. Previous purchases may not be restored if they are no longer in the iTunes Store, App Store, or iBookstore.
- Some previously purchased movies may not be available in iTunes in the Cloud. These movies will indicate that they are not available in iTunes in the Cloud on their product details page in the iTunes Store. Previous purchases may be unavailable if they have been refunded or are no longer available in the iTunes Store, App Store, or iBookstore.
You get 5 GB of free iCloud storage for:
- Photos and videos in the Camera Roll
- Device settings (for example: Phone Favorites, Wallpaper, and Mail, Contacts, Calendar accounts)
- App data
- Home screen and app organization
- Messages (iMessage, SMS, and MMS)
- Visual Voicemails