What is in the Other category on my iPhone storage?

I have an iPhone 4 (not 4s), and when i plug it into my computer, it says there's 3.5gb of Other, but i don't know what's in this "Other" category. I cleared all my web history/cache/cookies, and deleted tons and tons of emails along with all my text conversations and recent calls, but that barely did anything. What else can i do to reduce the size of this category?

Wish I had a dollar for everyone that asks this question…
If you still have the box, or paperwork from the iPhone… Note where is says how many GB the phone has… Then the print next to, or under it that says actual formatted space is less.

The "other" is the operating system on the phone, built in Apps, contact data, your personal data, etc.

Without "other", you have a paperweight with the Apple logo on it…