Managing Pairs of Web pages and folders

Windows XP
In Folder Options there are three choices for "Managing pairs of Web pages
and folders." They are:
- show and manage the pair as a single file
- show both parts and manage them individually
- show both parts but manage as a single file.

What does this mean?
Does it have anything to do with creating or maintaining a web?
Or is it something we do in Windows in general?
There is nothing in Windows Help files on this subject.