Server Side Includes (SSI) is a basic server-side language, which lets you include text from a specific source within a website. In the most popular situation, the text from a file is included in a different one, giving a website the sense that it's dynamic. For instance, in case your site is made of 10 web pages, five of them can easily include the content of some file, such as horoscope.txt. Any time you alter this text file, the new content is going to appear on all of the five webpages, which will help you revise your site faster and easier than if you had to change a part of all five pages. Server Side Includes is at times employed to contain the output of basic commands, scripts or functions as well - a hit counter that is shown on the website, the current time and date or the visitor's IP address. Every web page that utilizes SSI will need to have a unique extension - .shtml.