DirectoryIndex is the default page served by the server when a user requests an index of a directory by specifying a forward slash (/) at the end of the directory name.
When a user requests the page http://example/this_directory/, they get either the
DirectoryIndex page, if it exists, or a server-generated directory list. The default for
index.html and the
index.html.var type map. The server tries to find either of these files and returns the first one it finds. If it does not find one of these files and
Options Indexes is set for that directory, the server generates and returns a listing, in HTML format, of the subdirectories and files within the directory, unless the directory listing feature is turned off.