Server Side Includes (SSI) is a simple server-side language, which lets you include text from a specific source inside a website. In the most widespread case, the text from a file is incorporated in a different one, giving a site the sense that it's dynamic. For instance, in case your site has 10 web pages, five of them can include the content of any kind of file, like horoscope.txt. If you change this text file, the new content is going to appear on all five webpages, which shall enable you to bring up to date your website faster and easier than if you had to update a component of all 5 web pages. Server Side Includes is occasionally used to include the output of simple commands, scripts or functions as well - a hit counter that is shown on the site, the current date and time or the visitor's IP address. Every web page that works by using SSI must have a special extension - .shtml.