Default Web Page: Many URLs don’t actually have a file name at the end to indicate exactly which web page is being requested:
http://pages.uoregon.com/susanq/110/p2/
Since there is no file name at the end of the URL, your browser is actually requesting thedirectory of files that exists at this URL.
Web servers are configured to return the default page for that directory, if it contains a file with any of these names: index.html, index.htm, default.html, default.html.
If your directory does not contain a file of this name, your browser will display a listing of the directory’s contents.
Default web pages help to abbreviate URLs and, for security, can be used to prevent visitors from getting a directory list of files.