Other is on the iPad, not "in iTunes". (iTunes is simply showing you how the memory on the iPad is being used, it's an important distinction.)
Other is corrupt files, or anyhting else that the iPad cannot recognise. There is always a small quantity of Other, but 6.6GB is too much. Often a Sync with your iTunes Library will sort it out. However, you should note that while a Sync is taking place, the amount of Other can increase. On my iPod Touch, the Apps often get marked as Other for a short while during a Sync.
Personally, I avoid making changes to my Library/iPod while the Sync is taking place. I make my changes in the iTunes Library first, and the allow the Sync to copy the changes onto my iPod as a separate procedure. Otherwise, it's possible that moving media that iTunes is trying to move at the same time could cause errors.
Yours is one possible solution. I am seeing a flaw in the OS handling data in storage. If I delete an item from my ipad. That space should be released by the OS to be used by something else. One of the solutions I have seen was to do a restore. I don't think that is a good answer. It takes way to much time. The best I have found is to power cycle your device. This resets memory and clears space.
I thought you were asking what Other is (despite your lack of question mark at the end of your title), not telling us of the technical ins and outs of iTunes. Your post is marked as a question in the discussions list.
I'm still not sure what the purpose of your post was. If you want to tell Apple of a bug you've found, then perhaps http://www.apple.com/feedback/ would be useful.