In Sorting, What is Position?

When sorting products on a page, one (1st) option is Position and I can't possibly see what exactly does it mean. In our store it is the same as A-Z. Is it the same as Alphabetic? Why there are two then?

Thanks in advance and I did read Docs first and searched this Forum, there is no answer to that.

In category page, it is ProductCategory.DisplayOrder ASC
In manufacturer page, it is ProductManufacturer.DisplayOrder ASC
In other pages (vendor/search), it is Product.Name ASC

Thanks, so effectively Name A-Z which is already there, wonder why have it twice? ^_^

It's typically DisplayOrder

Anyone figure out how to sort by inventory?

custom sorts require code changes