What is this spinning circle next to the 3G icon on my iphone?

And is this why I'm using so much data. I'm visting Seattle been here for 5 days now and that spinning circle keeps spinning. Got a text last night saying I have used 75% of my data and then this morning I got another text saying I have used 90% of my data and I have not been do a whole lot on the internet.

But please my main question is what is that spinning circle next to the 3G icon on my iphone.

Maybe you left any app which uses Internet… There are two types of spinng circle. (1- loading data and (2-syncing.