What is a city holding?

[:Dhjaru:]

When playing i saw this thing in the top left corner of the pop menu. but i couldn't find a nation or a city with any holding... Please explain.

 

[tradetem]

one of my roman generals got a holding on an island after sieging it down and me annexing the place. I don't know what these do and they are kinda hidden in the interface.

 

[Peter Ebbesen]

A holding is the personal estate of a character and earns him income separate from his wages. It is gained by conquest as a general or by governing a region.