What is "other"

It is pretty much as the name implies.
All the things that don't fit under the usual things like anything you add to an outside app like PDF's to Goodreader or movies to VLC Or Goodplayer, Comics in a comics app and so on.
I also believe but am not sure the system files are under that too.

Hope this helps.

 

Game saves, porn.

 

It's food.

 

Other usually is the IOS install but sometimes when it fluctuates like that it's probably microscopic interdenominational aliens known as iQuark strings. They're harmless and need to feed on the extra power of the iPad to keep the warmth down buy the quadcore GPU Nothing to worry about - just Apple trying to help

 

Yes, Squidward. Food for the soul. Krabby Patties.

 

Other data is things like iOS OTA updates, Siri voice files, Safari data, stock app caches, system caches, iTunes media artwork, photo library databases (not the images themselves), text messages, picture/video messages, emails, rented videos that are expired but not deleted.

Not quite. If you add PDFs to Goodreader, they count as app data. If you add any data to an App Store app's sandbox folder, it counts as app data.

 

If it gets stuck on a large amount then it could be leftover crap from aborted syncs. In that case it's worth doing a full restore from backup which will only restore the stuff you're actually using.