Camera Roll, all the picture you have taken with your iPhone. They are include in the iPhone Backup but should be transfered to your iPhoto Library on the computer for a better back up. Just like in the old days with a film camera, the is like you iPhones roll of film.
Photo Stream is iCloud's way of sharing your photos between your devices. It is not permanent storage for photo's limited to 1000 photos and can be deleted automatically in 30 days. It is a handy way to veiw photos on an Apple TV and other iOS devices or a quick and simple way to transfer them into iPhoto on your computer with out having to connect your iPhone to the computer. These photos are not backed up other than being visible on all your devices.
The Photo Library contains all the photos you synced from your computer. They are not in any part a part of iCloud or it's back ups. Since these photos come from your computer they should be backed up using it's backup routine. These photos should be managed using iTunes to add and remove them.
Take a picture with your iPhone, the new photo will end up in Camera Roll and Photo Stream. Copy that photo to your iPhoto Library on the Mac either by connecting your iPhone or select the photo in Photo Stream in iPhoto and it will get copied back to your iPhone in it's Photo Library. Once in the Library and a more stable backup routine you are able to detele it from the Camera Roll to clean it up. The Photo Stream copy could be deleted or leave it there for viewing on other devices that may not have access to your iPhoto Library. I suspect we may be able to share Photostream.
