Overview
An index page is the page a Web server pulls up for a given directory if a filename is not specified. For example, http://yourdomain.com/ will scan the document root sequentially looking for the first file match. If found, that page will be displayed. By default, the directory index order of precedence is (in decreasing priority): index.html, index.php, index.shtml, index.htm, index.cgi, index.pl, and finally index.jsp. Going from left to right in the list, the first file found will serve as the directory index.
Changing Default Value
To specify home.html as the index page such that when a user accesses http://yourdomain.com/ it would be the same as accessing http://yourdomain.com/home.html, add the following line to your .htaccess file:
DirectoryIndex home.html
Caveats
Directory indexes apply recursively to all sub-directories. All subdirectories will inherit these rules. In order to reset the directory index list specify a new DirectoryIndex directive through an .htaccess file to any directories that reside within the directory in which the initial DirectoryIndex is applied.
Example:
Under /var/www/html/.htaccess:
DirectoryIndex home.html
Under /var/www/html/myapp:
DirectoryIndex index.html index.php index.shtml index.cgi
Such a setup can yield an unmaintainable hierarchy of .htaccess files. For this reason, usage of DirectoryIndex is discouraged.