what is "other" on my iphone 6 plus

When my iphone is connected to my computer and I go to Itunes, at the bottom there is a usage chart. it seems that other is taking up the most space on the computer, what is other and how do I change so there is more free space on the phone. When I open the storage tab on the phone, under photos and camera, it states there is 3.5 gigs being uses, I had thought that whenever I shot a video or still shot it went to the cloud so it didn't take up space on the phone

any suggestions