region > area > district

[keannu]

I think this might be hard to explain as every country's regional system is all different. But what is the standard to tell the three units? By size or what? My wild guess is like this by size. What does each word mean?
ex) region > area > district

 

[JohnParis]

That sounds about right to me.
As for the meanings of each, the best answers are in your dictionary. However, as you said, things vary from country to country.