Server Side Includes (SSI) is a basic server-side language, which allows you to incorporate text from a given source in a website. In the most widespread case, the text from a single file is included in a second one, providing a website the sense that it's dynamic. For instance, in case your website is made of ten webpages, five of them can have the content of some file, such as horoscope.txt. In case you modify this text file, the new content will come up on all five pages, which shall enable you to revise your website faster and easier than if you had to modify a component of all 5 pages. Server Side Includes is in some cases employed to incorporate the output of simple commands, scripts or functions as well - a hit counter that is shown on the website, the current date and time or the customer's IP address. Every webpage that utilizes SSI should have a unique extension - .shtml.