Server Side Includes (SSI) is a simple server-side language, which lets you include text from a specific source inside a web page. In the most popular scenario, the text from a file is incorporated in another, providing a site the feeling that it is dynamic. As an example, if your website comprises of ten web pages, 5 of them can contain the content of any kind of file, like horoscope.txt. In case you modify this text file, the new content will come up on all of the five webpages, which shall enable you to update your website much easier than if you had to modify part of all 5 web pages. Server Side Includes is at times employed to contain the output of simple commands, scripts or functions as well - a hit counter that's shown on the site, the current time and date or the visitor's IP address. Every webpage that employs SSI will need to have a special extension - .shtml.