Server Side Includes (SSI) is a basic server-side language, which lets you incorporate text from a given source in a website. In the most common situation, the text from a single file is included in another, giving a site the feeling that it is dynamic. As an example, if your website has 10 pages, five of them can easily include the content of some file, such as horoscope.txt. If you change this text file, the updated content will come up on all of the five web pages, which will enable you to revise your site faster and easier than if you had to modify an element of all 5 web pages. Server Side Includes is occasionally utilized to incorporate the output of basic commands, scripts or functions as well - a hit counter that's displayed on the website, the present time and date or the visitor's IP address. Every web page that uses SSI should have a particular extension - .shtml.