explain the concept of ssi
Server Side Includes (SSI) are commands and directives placed in Web pages that are evaluated by the Web server when the Web page is being served. SSI are not supported by all web servers. So before using SSI read the web server documentation for the support. SSI is useful when you want a small part of the page to be dynamically generated rather than loading the whole page again.
The Server Side Includes is a simple interpreted server side scripting used in HTML pages to make it more responsive web pages on web server. SSI enables the HTML pages to add one or more files into a web page and come out with given directives. The SSI makes easy to maintain the site.