How can I tell what "Audio" and "Other" contains in iTunes's iOS device capacity meter? In iTunes, when selecting an iOS device from the left pane, the user is presented with a bar graph along the bottom of the primary pane showing the used space and available space of the given device. 



In this example, the iPad in question contains no songs. My music is all synced through iTunes Match and I have not downloaded any songs (because of my lack of available space). How can I know what that 8.3 GB of audio is? On my iPhone I had assumed it was things like downloaded Audible books, but that can't be the case as Audible's app is not universal, and I haven't installed it on my iPad so there are no Audible books on my device. I do have podcasts synced to my device through iTunes ("Automatically include all unplayed episodes of all podcasts"), but the total size of all synced episodes (~2 GB) is far less than the stated use of 8.3 GB.

And what is included in "Other"? Is that data that apps use for offline storage (such as Instapaper articles and offline Evernote notebooks)? Or would those items be counted under Apps as they are stored in apps' respective folders on the device?

How can I nail down exactly what is using the space on my iOS devices with such ambiguous category names? Secondarily, how are apps' internal storage counted in this graph? For example, the previously stated Instapaper articles, Evernote's offline notebooks: "Apps" or "Other"? Audible's downloaded audiobooks: "Apps", "Audio", "Books", or "Other"? Camera+'s internal photo "Lightbox" feature: "Apps", "Photos", or "Other"?
The other part of the graph, as far as I know, consists of caches, cookies, history, logs, ... (mostly from safari). Also, things like contacts, calender events, ... are in this part, too. I don't think any app document (like Evernote's or Instapaper's) goes to this part. It's all in the app part. 

So, for example, it can be cleared up a good amount by going to safari settings and clearing all caches, history, ... You'll be amazed at how much space they've claimed!

About the audio, it is really strange that with no music and some audiobooks, it have taken up so much space. I don't know any other stuff other than that to be included in that part.

As a side note, sometimes doing a resync in iTunes will change the graph. Sometimes even the other part shrinks and goes to apps. So maybe you can try and see what happens.

Hope it helps.