What is 'other' data?

There is a long running thread about this on apple discussion forums with a bunch of varied comments. If a thread on this exists here can someone please direct me to it?

If not here goes... So when I'm synching some new songs into my iPhone the data marked as 'other' has crept up to almost 2.5gb. Is there any official word from apple on what this is and how it's size varies?

My iPhone is 32gb anyway and I still have around 14gb free but the fact that this is so high is annoying me. Is this normal?

Btw I have an iPhone 5c and it's running the latest fw 7.x I can't remember the latest.

Thanks