Server Side Includes (SSI) is a basic server-side language, which allows you to include text from a given source in a website. In the most widespread situation, the text from a file is integrated in a second one, giving a site the feeling it is dynamic. As an example, in case your website comprises of 10 webpages, 5 of them can contain the content of any kind of file, for example horoscope.txt. As soon as you alter this text file, the modified content is going to appear on all five pages, which will permit you to bring up to date your site faster and easier than if you had to modify an element of all five web pages. Server Side Includes is in some cases used to include the output of simple commands, scripts or functions as well - a hit counter that's shown on the website, the current time and date or the visitor's IP address. Any web page that works by using SSI must have a special extension - .shtml.