Those are actually directories that are loading the default webpage.
All web servers have the ability to define a default page. Common examples
are:
index.htm
index.html
default.htm
default.html
home.htm
home.html
The list of files varies from server to server, this is not an exhaustive
list.
The purpose of the default document is that whenever you enter a URL that
points to a directory, such as in your example, without specifying a
document (or filename), the web server will basically look in the directory
for any file that matches it's list of defaults. If it finds one, it
automatically sends that to the requesting browser.
The list of default documents also determines the order that the server
looks for filenames. Basically, it starts at the top and goes sequentially
through the list, serving up the first match it finds. Using the list from
above, if you had a directory that had both "index.htm" and "default.htm",
index.htm would always be served automatically since it's first in the list.
Normally, to avoid confusion, it's recommended that you only have one
default file in any directory.
This default document system allows a visitor to enter a URL such as
www.example.com and get a webpage, without having to type in specific page
names, or know what the default filename is on any web server. This same
functionality extends to subdirectories within a site.
If you have subdirectories such as:
www.example.com/about/
www.example.com/contact/
www.example.com/products/
and you put a default document in those directories, visitors only need to
know the "shorter, friendlier" name as shown above.
So the short answer is, find out what the default file name is on your web
server, and be sure to add a file to each directory that uses this name.
You could even have directories with a single default file in them if you
want, though that puts a ton of directories in your site and could make
managing your site a little more difficult. But it is an option and I'm
certain there are many sites out there that do exactly this so all their
pages have "extensionless" pages.
