Along with Audio, Photos, Apps, Books, there is Other space available on your iPhone.
Let’s say that you have an iPhone, 16GB model. To know how much space is occupied by Other, launch the iTunes Player. Make sure that you have connected your iPhone to your computer. From the iTunes Player, go to your device, and at the bottom of the iTunes window you will notice the iPhone’s disk space.
In my case, my iPhone 4S has 4.5 GB of data stored in Other. You can always reclaim this space by removing the temporary files and games that automatically saves data.
The Other storage space shown on your iTunes window is usually cache and app-related files. For instance, when you save a game on an iPhone, the data will be stored in Other. When you upgrade your iPhone to a newer iOS, Other will have system cache files stored
Some of the jailbroken iPhone users have said that iTunes only shows Other space. This means the storage graph doesn’t show the space occupied by audio, photos or books.
The solution to this problem is simple. You have to unplug your iPhone, respring it, and plug it back in the computer. You can also hit the Sync button on your iTunes to bring everything back to normal. Resyncing can also remove partially downloaded apps, ultimately freeing up your iPhone’s space.
If you are looking for recovering your iPhone’s storage space, check out iCleaner, a useful Cydia app that removes junk and useless files from an iPhone.