What is SSI ?
SSI (Server Side Includes) are directives that are placed in HTML pages, and evaluated on the server while the pages are being served. They let you add dynamically generated content to an existing HTML page, without having to serve the entire page via a CGI program, or other dynamic technology.To permit SSI on your server, you must have mod_include installed and enabled. Additionally, you must have the above directive either in your httpd.conf file, or in a .htaccess file. You should place the following lines in the .htaccess file to allow SSI directives to be included in the .html or .htm files

AddHandler server-parsed .html
AddHandler server-parsed .htm
AddType text/html html