Server Side Includes (SSI) is a basic server-side language, which lets you include text from a specified source within a web page. In the most common case, the text from a file is included in a different one, giving a site the sense that it is dynamic. As an example, in case your site has ten web pages, five of them can include the content of some file, like horoscope.txt. Any time you modify this text file, the new content will appear on all five pages, which shall allow you to update your site faster and easier than if you had to modify a component of all 5 web pages. Server Side Includes is in some cases used to include the output of basic commands, scripts or functions as well - a hit counter that's shown on the site, the present date and time or the customer's IP address. Any web page that employs SSI should have a particular extension - .shtml.