What does "Other" mean in data usage for iPhone storage?

I have a 32 GB iPhone 5S and when I got it, I did NOT restore it from a backup and when I plugged in my phone to sync music, it says:

Audio: 8.94 GB

Photos: 6.37 GB

Apps: 1.48 GB

Documents and Data: 648.2 MB

Other: 7.08 GB

What's the other category consist of and how do I delete its data?