Server Side Includes (SSI) is a simple server-side language, which enables you to include text from a specific source in a website. In the most popular case, the text from one file is incorporated in a second one, giving a site the sense that it is dynamic. For instance, in case your website is comprised of ten webpages, five of them can easily contain the content of any kind of file, for example horoscope.txt. As soon as you modify this text file, the updated content is going to appear on all five web pages, which shall help you bring up to date your website much easier than if you had to modify an element of all five web pages. Server Side Includes is at times used to incorporate the output of basic commands, scripts or functions as well - a hit counter that is shown on the site, the present date and time or the visitor's IP address. Every webpage that uses SSI should have a special extension - .shtml.