iPad Storage : ‘Other’ ?

I have an iPad Air that is constantly showing ‘storage nearly full’ alerts.

I have deleted lots of photos (and then emptied the ’Recently Deleted‘ folder to be sure that they are gone) and offloaded unused apps.

If I go into Settings and analyse storage usage (Settings>General>Ipad Storage):

Approx’ half of the 29gb used (of 32gb) is showing as ’Other’. What is this content?

It possibly corresponds to 14gb showing as ‘System’? (listed at the bottom of the list of apps).