Server Side Includes (SSI) is a basic server-side language, which allows you to include text from a given source inside a web page. In the most typical situation, the text from one file is included in a different one, giving a website the sense it is dynamic. For instance, in case your website is comprised of ten webpages, 5 of them can contain the content of some file, like horoscope.txt. As soon as you alter this text file, the modified content will appear on all of the five webpages, which shall let you revise your site faster and easier than if you had to modify a part of all 5 pages. Server Side Includes is sometimes employed to include 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 must have a particular extension - .shtml.